Currently when runing under KVM on ppc, we synchronize a certain number of
vital SPRs to KVM through the SET_SREGS call.  This leaves out quite a lot
of important SPRs which are maintained in KVM.  It would be helpful to
have their contents in qemu for debugging purposes, and when we implement
migration it will be vital, since they include important guest state that
will need to be restored on the target.

This patch sets up for synchronization of any registers supported by the
KVM ONE_REG calls.  A new variant on spr_register() allows a ONE_REG id to
be stored with the SPR information.  When we set/get information to KVM
we also synchronize any SPRs so registered.

For now we set this mechanism up to synchronize a handful of important
registers that already have ONE_REG IDs, notably the DAR and DSISR.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>