qxl: prepare memslot code for suspend/resume

this splits out initing the hw memslots from the guest info, and
creates an entrypoint for s/r to use.

Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --cc drivers/gpu/drm/qxl/qxl_drv.h
Simple merge

diff --cc drivers/gpu/drm/qxl/qxl_kms.c
Simple merge