drm/i915: Request full SSEU enablement on Gen9

drm/i915: Request full SSEU enablement on Gen9

On Gen9 the render power gating can leave slice/subslice/EU in
a partially enabled state. We must make an explicit request for
full SSEU enablement through the Render Power Clock State
register when resuming render work. This register is save/
restored in the logical ring context image for execlist
submission mode. Initialize its value in each LRC image to
request full enablement according to the device SSEU config.

Thanks to Sharma Ankitprasad and Akash Goel for highlighting the
issue and proposing the initial fix on which this patch is based.

v2: Adjusted the names of the power gating support flags to fit
    update of an earlier patch.

Signed-off-by: Jeff McGee <jeff.mcgee@intel.com>
Reviewed-by: "Akash Goel <akash.goel@intel.com>"
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>