powerpc/xmon: Add AMR, UAMOR, AMOR, IAMR to SPR dump

This patch adds support to xmon for dumping the AMR, UAMOR, AMOR and
IAMR SPRs based on their supported ISA revisions.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
[mpe: Split out of larger patch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>