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

tools/cert_create/include/cert.h

@@ -57,6 +57,7 @@ struct cert_s {
 	const char *opt;	/* Command line option to pass filename */
 	const char *fn;		/* Filename to save the certificate */
 	const char *cn;		/* Subject CN (Company Name) */
+	const char *help_msg;	/* Help message */
 
 	/* These fields must be defined statically */
 	int key;		/* Key to be signed */

tools/cert_create/include/cmd_opt.h

@@ -42,9 +42,16 @@ enum {
 	CMD_OPT_EXT
 };
 
+/* Structure to define a command line option */
+typedef struct cmd_opt_s {
+	struct option long_opt;
+	const char *help_msg;
+} cmd_opt_t;
+
 /* Exported API*/
-int cmd_opt_add(const char *name, int has_arg, int val);
+void cmd_opt_add(const cmd_opt_t *cmd_opt);
 const struct option *cmd_opt_get_array(void);
 const char *cmd_opt_get_name(int idx);
+const char *cmd_opt_get_help_msg(int idx);
 
 #endif /* CMD_OPT_H_ */

tools/cert_create/include/ext.h

@@ -50,6 +50,7 @@ typedef struct ext_s {
 	const char *oid;	/* OID of the extension */
 	const char *sn;		/* Short name */
 	const char *ln;		/* Long description */
+	const char *help_msg;	/* Help message */
 	int asn1_type;		/* OpenSSL ASN1 type of the extension data.
 				 * Supported types are:
 				 *   - V_ASN1_INTEGER

tools/cert_create/include/key.h

@@ -64,6 +64,7 @@ enum {
 typedef struct key_s {
 	int id;			/* Key id */
 	const char *opt;	/* Command line option to specify a key */
+	const char *help_msg;	/* Help message */
 	const char *desc;	/* Key description (debug purposes) */
 	char *fn;		/* Filename to load/store the key */
 	EVP_PKEY *key;		/* Key container */