drm/amdgpu: remove unused functions

AMDGPU statically sets priority for compute queues
at initialization so remove all the functions
responsible for changing compute queue priority dynamically.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>