drm/amdgpu: cleanup struct amdgpu_ring

drm/amdgpu: cleanup struct amdgpu_ring

This patch consist of below related changes:

1 Rename ring->priority to ring->hw_prio.
2 Assign correct hardware ring priority.
3 Remove ring->priority_mutex as ring priority remains unchanged
  after initialization.
4 Remove unused ring->num_jobs.

v3: remove ring->num_jobs.
v2: remove ring->priority_mutex.

Fixes: 936c043de716 ("drm/amdgpu: set compute queue priority at mqd_init")
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>