Set empty usage field for commands that do not need parameters

The missing field causes runtime debug message
	BUG: command '%s' does not have the '.usage' field filled out

While there, fix some minor typo in the help messages:
	s/deasert/deassert/
	s/Deasert/Deassert/

Change-Id: If3dd18265cda103ca0d05609f67f4ca58e7cbb27
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5024
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/flash/nor/at91sam3.c

@@ -3731,6 +3731,7 @@ static const struct command_registration at91sam3_exec_command_handlers[] = {
 		.mode = COMMAND_EXEC,
 		.help = "Print information about the current at91sam3 chip"
 			"and its flash configuration.",
+		.usage = "",
 	},
 	{
 		.name = "slowclk",

src/flash/nor/at91sam4.c

@@ -3212,6 +3212,7 @@ static const struct command_registration at91sam4_exec_command_handlers[] = {
 		.mode = COMMAND_EXEC,
 		.help = "Print information about the current at91sam4 chip"
 			"and its flash configuration.",
+		.usage = "",
 	},
 	{
 		.name = "slowclk",

src/flash/nor/at91sam4l.c

@@ -668,7 +668,8 @@ static const struct command_registration at91sam4l_exec_command_handlers[] = {
 		.name = "smap_reset_deassert",
 		.handler = sam4l_handle_reset_deassert,
 		.mode = COMMAND_EXEC,
-		.help = "deasert internal reset held by SMAP"
+		.help = "deassert internal reset held by SMAP",
+		.usage = "",
 	},
 	COMMAND_REGISTRATION_DONE
 };

src/flash/nor/at91samd.c

@@ -1217,7 +1217,8 @@ static const struct command_registration at91samd_exec_command_handlers[] = {
 		.name = "dsu_reset_deassert",
 		.handler = samd_handle_reset_deassert,
 		.mode = COMMAND_EXEC,
-		.help = "Deasert internal reset held by DSU."
+		.help = "Deassert internal reset held by DSU.",
+		.usage = "",
 	},
 	{
 		.name = "info",
@@ -1225,6 +1226,7 @@ static const struct command_registration at91samd_exec_command_handlers[] = {
 		.mode = COMMAND_EXEC,
 		.help = "Print information about the current at91samd chip "
 			"and its flash configuration.",
+		.usage = "",
 	},
 	{
 		.name = "chip-erase",
@@ -1232,6 +1234,7 @@ static const struct command_registration at91samd_exec_command_handlers[] = {
 		.mode = COMMAND_EXEC,
 		.help = "Erase the entire Flash by using the Chip-"
 			"Erase feature in the Device Service Unit (DSU).",
+		.usage = "",
 	},
 	{
 		.name = "set-security",

src/flash/nor/atsame5.c

@@ -893,12 +893,14 @@ COMMAND_HANDLER(samd_handle_reset_deassert)
 static const struct command_registration same5_exec_command_handlers[] = {
 	{
 		.name = "dsu_reset_deassert",
+		.usage = "",
 		.handler = samd_handle_reset_deassert,
 		.mode = COMMAND_EXEC,
 		.help = "Deasert internal reset held by DSU."
 	},
 	{
 		.name = "chip-erase",
+		.usage = "",
 		.handler = same5_handle_chip_erase_command,
 		.mode = COMMAND_EXEC,
 		.help = "Erase the entire Flash by using the Chip-"

src/flash/nor/kinetis.c

@@ -3127,6 +3127,7 @@ static const struct command_registration kinetis_exec_command_handlers[] = {
 		.mode = COMMAND_CONFIG,
 		.help = "Driver creates additional banks if device with two/four flash blocks is probed",
 		.handler = kinetis_create_banks_handler,
+		.usage = "",
 	},
 	COMMAND_REGISTRATION_DONE
 };

src/flash/nor/nrf5.c

@@ -1118,6 +1118,7 @@ static const struct command_registration nrf5_exec_command_handlers[] = {
 		.handler	= nrf5_handle_mass_erase_command,
 		.mode		= COMMAND_EXEC,
 		.help		= "Erase all flash contents of the chip.",
+		.usage		= "",
 	},
 	COMMAND_REGISTRATION_DONE
 };

src/flash/nor/numicro.c

@@ -1856,6 +1856,7 @@ static const struct command_registration numicro_exec_command_handlers[] = {
 		.handler = numicro_handle_chip_erase_command,
 		.mode = COMMAND_EXEC,
 		.help = "chip erase through ISP.",
+		.usage = "",
 	},
 	COMMAND_REGISTRATION_DONE
 };

src/flash/nor/tcl.c

@@ -1239,12 +1239,14 @@ static const struct command_registration flash_config_command_handlers[] = {
 		.mode = COMMAND_CONFIG,
 		.handler = handle_flash_init_command,
 		.help = "Initialize flash devices.",
+		.usage = "",
 	},
 	{
 		.name = "banks",
 		.mode = COMMAND_ANY,
 		.handler = handle_flash_banks_command,
 		.help = "Display table with information about flash banks.",
+		.usage = "",
 	},
 	{
 		.name = "list",