Some of the 64bit PPC CPU features are MMU-related, so this patch moves
them to MMU_FTR_ bits.  All cpu_has_feature()-style tests are moved to
mmu_has_feature(), and seven feature bits are freed as a result.
Signed-off-by: NMatt Evans <matt@ozlabs.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>