drm/amdgpu/vg20:Restruct uvd.inst to support multiple instances

Vega20 has dual-UVD. Need add multiple instances support for uvd.
Restruct uvd.inst, using uvd.inst[0] to replace uvd.inst->.
Repurpose amdgpu_ring::me for instance index, and initialize to 0.
There are no any logical changes here.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
index 49cad08..c6850b6 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
@@ -362,6 +362,7 @@ void amdgpu_ring_fini(struct amdgpu_ring *ring)
 
 	dma_fence_put(ring->vmid_wait);
 	ring->vmid_wait = NULL;
+	ring->me = 0;
 
 	ring->adev->rings[ring->idx] = NULL;
 }