target/ppc: Add function to get protection key for hash32 MMU

Add a function to get key bit from SR and use it instead of open coded
version.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
3 files changed