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

Remove asic/vega10/UMC folder.

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>