ARM: 5888/1: arm: Update comments in cacheflush.h and remove unnecessary V6 and V7 comments

The comments in cacheflush.h should follow what's in
struct cpu_cache_fns. The comments for V6 and V7 are
unnecessary.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>