drm/i915: Terminate the FORCE WAKE after we have finished reading

Once we have read the value out of the GT power well, we need to remove
the FORCE WAKE bit to allow the system to auto-power down.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

diff --cc drivers/gpu/drm/i915/i915_drv.c
Simple merge

diff --cc drivers/gpu/drm/i915/i915_drv.h
Simple merge

diff --cc drivers/gpu/drm/i915/i915_reg.h
Simple merge