drm/amdgpu: for S0ix, skip SDMA 5.x+ suspend/resume

SDMA 5.x is part of the GFX block so it's controlled via
GFXOFF.  Skip suspend as it should be handled the same
as GFX.

v2: drop SDMA 4.x.  That requires special handling.

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