drm/amdgpu/vcn2.5: Add firmware w/r ptr reset sync

Add firmware write/read point reset sync through shared memory

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>