ARM: 7861/1: cacheflush: consolidate single-CPU ARMv7 cache disabling code

This code is becoming duplicated in many places.  So let's consolidate
it into a handy macro that is known to be right and available for reuse.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>