ARM: 5995/1: ARM: Add L2x0 outer_sync() support (3/4)

The L2x0 cache controllers need to explicitly drain their write buffer
even for Normal Noncacheable memory accesses.

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