Remove several warnings reported with W=1

Improved support for W=1 compilation flag by solving missing-prototypes
and old-style-definition warnings.

The libraries are compiling with warnings (which turn into errors with
the Werror flag).

Outside of libraries, some warnings cannot be fixed without heavy
structural changes.

Change-Id: I1668cf99123ac4195c2a6a1d48945f7a64c67f16
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
diff --git a/include/drivers/console.h b/include/drivers/console.h
index 24887f9..4f26cce 100644
--- a/include/drivers/console.h
+++ b/include/drivers/console.h
@@ -49,11 +49,12 @@
 #include <drivers/console_assertions.h>
 
 /*
- * NOTE: There is no publicly accessible console_register() function. Consoles
- * are registered by directly calling the register function of a specific
- * implementation, e.g. console_16550_register() from <uart_16550.h>. Consoles
- * registered that way can be unregistered/reconfigured with below functions.
+ * Add a console_t instance to the console list. This should only be called by
+ * console drivers after they have initialized all fields in the console
+ * structure. Platforms seeking to register a new console need to call the
+ * respective console__register() function instead.
  */
+int console_register(console_t *console);
 /* Remove a single console_t instance from the console list. Return a pointer to
  * the console that was removed if it was found, or NULL if not. */
 console_t *console_unregister(console_t *console);