ppc64: Extract copy to protobuf functions

Since the Transactional memory state will contains VSX, VMX and FP
registers, extracting the common code copying data to protobuf buffer in
separate functions.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>