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>

arch/arm/mm/cache-l2x0.c

 /*
- * arch/arm/mm/cache-l2x0.c - L210/L220 cache controller support
+ * arch/arm/mm/cache-l2x0.c - L210/L220/L310 cache controller support
  *
  * Copyright (C) 2007 ARM Limited
  *