drm/amdgpu: enable gfxoff again on raven series (v2)

This patch enables gfxoff and stutter mode again, since we take more testing on
raven series. For raven2 and picasso, we can enable it directly. And for raven,
we need check the RLC/SMC ucode version cannot be less than #531/0x1e45.

v2: add smc version checking for raven.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Tested-by: Likun Gao <Likun.Gao@amd.com> (v2)
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>