drm/amd/amdgpu: add raven1 part to the gfxoff quirk list

On my raven1 system (rev c6) with VBIOS 113-RAVEN-114 GFXOFF is
not stable (resulting in large block tiling noise in some applications).

Disabling GFXOFF via the quirk list fixes the problems for me.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org