flash/nor: consolidate flash protect/protect_check

Make flash_driver methods protect() and protect_check()
optional.

Remove dummy definitions of these methods from the drivers
which do not implement protection handling.

Some drivers did not define protect method. It raised segfault
before this change and now it is handled properly.

Lot of drivers returned ERROR_OK from dummy protect()
- now flash_driver_protect() returns an error if not handled by the driver.

Change-Id: I2d4a0da316bf03c6379791b1b1c6198fbf22e66c
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4765
Tested-by: jenkins
Reviewed-by: Andreas Bolsch <hyphen0break@gmail.com>
Reviewed-by: Christopher Head <chead@zaber.com>

src/flash/nor/fm4.c

@@ -537,11 +537,6 @@ static int fm4_auto_probe(struct flash_bank *bank)
 	return fm4_probe(bank);
 }
 
-static int fm4_protect_check(struct flash_bank *bank)
-{
-	return ERROR_OK;
-}
-
 static int fm4_get_info_command(struct flash_bank *bank, char *buf, int buf_size)
 {
 	struct fm4_flash_bank *fm4_bank = bank->driver_priv;
@@ -714,7 +709,6 @@ struct flash_driver fm4_flash = {
 	.info = fm4_get_info_command,
 	.probe = fm4_probe,
 	.auto_probe = fm4_auto_probe,
-	.protect_check = fm4_protect_check,
 	.read = default_flash_read,
 	.erase = fm4_flash_erase,
 	.erase_check = default_flash_blank_check,