drm/amdgpu: soc15 enable (v3)

Add soc15 support and enable all the IPs for vega10.

v2: squash in xclk fix
v3: disable HDP MGCG

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