cert_create: update help message

The help message printed by the cert_create tool using the command
line option -h (or --help) does not correctly list all the available
command line options.

This patch reworks the print_help() function to print the help
messages in a data driven approach. For each command line option
registered, an optional help message can be specified, which will
be printed by print_help().

Help messages for the TBBR options (certificates, keys and images)
are also provided.

Fix a small bug in the short options string passed to getopt_long:
the ':' was missing in the '-a' option (this option must take an
argument).

Fixes ARM-software/tf-issues#337

Change-Id: I9d08c2dfd349022808fcc884724f677eefdc1452
diff --git a/tools/cert_create/src/tbbr/tbb_key.c b/tools/cert_create/src/tbbr/tbb_key.c
index 089425a..1d2f789 100644
--- a/tools/cert_create/src/tbbr/tbb_key.c
+++ b/tools/cert_create/src/tbbr/tbb_key.c
@@ -39,36 +39,43 @@
 	[ROT_KEY] = {
 		.id = ROT_KEY,
 		.opt = "rot-key",
+		.help_msg = "Root Of Trust key (input/output file)",
 		.desc = "Root Of Trust key"
 	},
 	[TRUSTED_WORLD_KEY] = {
 		.id = TRUSTED_WORLD_KEY,
 		.opt = "trusted-world-key",
+		.help_msg = "Trusted World key (input/output file)",
 		.desc = "Trusted World key"
 	},
 	[NON_TRUSTED_WORLD_KEY] = {
 		.id = NON_TRUSTED_WORLD_KEY,
 		.opt = "non-trusted-world-key",
+		.help_msg = "Non Trusted World key (input/output file)",
 		.desc = "Non Trusted World key"
 	},
 	[SCP_FW_CONTENT_CERT_KEY] = {
 		.id = SCP_FW_CONTENT_CERT_KEY,
 		.opt = "scp-fw-key",
+		.help_msg = "SCP Firmware Content Certificate key (input/output file)",
 		.desc = "SCP Firmware Content Certificate key"
 	},
 	[SOC_FW_CONTENT_CERT_KEY] = {
 		.id = SOC_FW_CONTENT_CERT_KEY,
 		.opt = "soc-fw-key",
+		.help_msg = "SoC Firmware Content Certificate key (input/output file)",
 		.desc = "SoC Firmware Content Certificate key"
 	},
 	[TRUSTED_OS_FW_CONTENT_CERT_KEY] = {
 		.id = TRUSTED_OS_FW_CONTENT_CERT_KEY,
 		.opt = "tos-fw-key",
+		.help_msg = "Trusted OS Firmware Content Certificate key (input/output file)",
 		.desc = "Trusted OS Firmware Content Certificate key"
 	},
 	[NON_TRUSTED_FW_CONTENT_CERT_KEY] = {
 		.id = NON_TRUSTED_FW_CONTENT_CERT_KEY,
 		.opt = "nt-fw-key",
+		.help_msg = "Non Trusted Firmware Content Certificate key (input/output file)",
 		.desc = "Non Trusted Firmware Content Certificate key"
 	}
 };