drm/amdgpu: remove some old gc 9.x registers

Leftover from bring up.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/amd/include:cleanup vega10 gc header files.

Cleanup asic_reg/vega10/GC folder.

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>