ARM: outer cache: add WARN_ON() to outer_disable()

Add WARN_ON() conditions to outer_disable() to ensure that its
requirements aren't violated.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --cc arch/arm/include/asm/outercache.h
Simple merge

diff --cc arch/arm/mm/Makefile
Simple merge

diff --cc arch/arm/mm/l2c-common.c
Simple merge