KVM: PPC: e500: Expose MMU registers via ONE_REG

MMU registers were exposed to user-space using sregs interface. Add them
to ONE_REG interface using kvmppc_get_one_reg/kvmppc_set_one_reg delegation
mechanism.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>