Add host2guc interface to notify GuC power state changes when
enter or resume from power saving state.

v3: Move intel_guc_suspend to i915_drm_suspend for consistency.

v2: Add GuC suspend/resume to runtime suspend/resume too

v1: Change to a more flexible way when fill host to GuC scratch
data in order to remove hard coding.
Signed-off-by: Alex Dai <yu.dai@intel.com>
Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>