drm/amdgpu: split gc v9_4_3 functionality from gc v9_0

To prepare for gc v9_4_3 specific feature.

v2: fix exports (Alex)

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>