Driver need to  poll the SURFACE_INUSE register to determine when to
start the new task and write data to the checked surface.

Implement the wait functions, and add the necessary hubbub registers.
Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>