ARM: v6/v7 cache: allow cache calls to be optimized

The v6 cache call optimization was disabled to allow the optional block
cache operations to be subsituted on CPUs which supported those
operations.  However, as that functionality was removed, we no longer
need to prevent this optimization being taken advantage of.

The v7 cache call optimization was just a copy of the v6, so also fix
that too.

Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>