MIPS: Kconfig: Rename SNIPROM too

CONFIG_SNIPROM was renamed to CONFIG_FW_SNIPROM in v3.8. Let's rename
SNIPROM itself too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-mips@linux-mips.org;
Cc: linux-kernel@vger.kernel.org
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>