cache.c does not work properly for aarch64. We create a struct cache_fns
using C preprocessor foo which assumes the existence of cache
maintenance operations with a certain name. These functions have other
names on aarch64. While we could fix this we do not need the automatic
cache function selection on aarch64 since here we only have one function
set.
Create a separate file and be done with this issue.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>