drm/i915: Update overlay code to do explicit request management

The overlay update code path to do explicit request creation and submission
rather than relying on the OLR to do the right thing.

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Tomas Elf <tomas.elf@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>