stdio_names: Ensure MAX_NAMES is defined before use, don't use 3 directly

With tighter build flags the fact that <stdio_dev.h> doesn't have a
reference back to MAX_NAMES causes an error.  Include <stdio.h> here and
then in common/console.c use MAX_NAMES rather than 3 when working with
stdio_names.

Reported-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>