drm/amdgpu/gfx9: drop duplicate gfx info init (v3)

Taken care of by gpu info firmware now.

v2: rebase
v3: rework based on latest firmware

Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Tested-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>