ARM: mm: Remove Kconfig symbol CACHE_PL310

Commit 20e783e3 ("ARM: 8296/1: cache-l2x0: clean up aurora cache
handling") removed the only user of the Kconfig symbol CACHE_PL310.
Setting CACHE_PL310 is now pointless. Remove its Kconfig entry, and one
select of this symbol.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>