drm/amdgpu: implement patch for fixing a known bug

Implement a patch to maunally reset read pointer

v2: using ring assignment instead of amdgpu_ring_write. adding comments
for each steps in the patch function.
v3: fixing a typo bug.
v4: fixing a bug in v3.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>