powerpc/64: More definitions for POWER9

This adds definitions for bits in the DSISR register which are used
by POWER9 for various translation-related exception conditions, and
for some more bits in the partition table entry that will be needed
by KVM.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>