ARM: 5993/1: ARM: Move the outer_cache definitions into a separate file (1/4)

To avoid #include collisions with subsequent patches in the series, this
patch moves the outer_cache definitions to a separate asm/outercache.h
file.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>