drm/amdgpu: During s0ix don't wait to signal GFXOFF

In the rare event when GFX IP suspend coincides with a s0ix entry, don't
schedule a delayed work, instead signal PMFW immediately to allow GFXOFF
entry. GFXOFF is a prerequisite for s0ix entry. PMFW needs to be
signaled about GFXOFF status before amd-pmc module passes OS HINT
to PMFW telling that everything is ready for a safe s0ix entry.

Bug: drm/amd#1712



Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>