x86: cpa, only flush the cache if the caching attributes have changed

We only need to flush the caches in cpa() if the the caching attributes
have changed. Otherwise only flush the TLBs.

This checks the PAT bits too although they are currently not used by
the kernel.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>