ARM7/ARM9: help/usage updates

Provide helptext which was sometimes missing; update some of it
to be more accurate.

Usage syntax messages have the same EBNF as the User's Guide;
there should be no angle brackets in either place.

Fix the User's Guide in a few places to be more consistent (mostly
to use brackets not parentheses) and to recognize that parameter may
be entirely optional (in which case the command just displays output,
and changes nothing).  Also reference NXP, not Philips, for LPC chips.

Don't use "&function"; functions are like arrays, their address
is their name.  Shrink some overlong lines.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/arm7_9_common.c

@@ -2864,32 +2864,32 @@ int arm7_9_init_arch_info(struct target *target, struct arm7_9_common *arm7_9)
 static const struct command_registration arm7_9_any_command_handlers[] = {
 	{
 		"dbgrq",
-		.handler = &handle_arm7_9_dbgrq_command,
+		.handler = handle_arm7_9_dbgrq_command,
 		.mode = COMMAND_ANY,
-		.usage = "<enable|disable>",
+		.usage = "['enable'|'disable']",
 		.help = "use EmbeddedICE dbgrq instead of breakpoint "
 			"for target halt requests",
 	},
 	{
 		"fast_memory_access",
-		.handler = &handle_arm7_9_fast_memory_access_command,
+		.handler = handle_arm7_9_fast_memory_access_command,
 		.mode = COMMAND_ANY,
-		.usage = "<enable|disable>",
+		.usage = "['enable'|'disable']",
 		.help = "use fast memory accesses instead of slower "
 			"but potentially safer accesses",
 	},
 	{
 		"dcc_downloads",
-		.handler = &handle_arm7_9_dcc_downloads_command,
+		.handler = handle_arm7_9_dcc_downloads_command,
 		.mode = COMMAND_ANY,
-		.usage = "<enable | disable>",
+		.usage = "['enable'|'disable']",
 		.help = "use DCC downloads for larger memory writes",
 	},
 	{
 		"semihosting",
-		.handler = &handle_arm7_9_semihosting_command,
+		.handler = handle_arm7_9_semihosting_command,
 		.mode = COMMAND_EXEC,
-		.usage = "<enable | disable>",
+		.usage = "['enable'|'disable']",
 		.help = "activate support for semihosting operations",
 	},
 	COMMAND_REGISTRATION_DONE