x86: merge mmu{,_32,_64}.h

Merge mmu_32.h and mmu_64.h into mmu.h.

Signed-off-by: Chris Snook <csnook@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>