Revert "drm/amdgpu: disallow gfxoff until GC IP blocks complete s2idle resume"

This reverts commit f543d286.

This is no longer needed since we no longer touch SDMA 5.x for s0i3.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>