ARM: cache-l2x0.c: Make it clear that cache-l2x0 handles L310 cache controller

It is not clear from the filename, and comment at the begining adds to the
confusion by not listing L310. Fix it.

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>