drm/amdgpu/gfx11: Adjust gfxoff before powergating on gfx11 as well

(Bas: speculative change to mirror gfx10/gfx9)

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>