drm/amd/display: Refactor watermark programming

* Replace certain register writes with register sets that overwrites the
  the entire register, instead of only a field within the register.
* Add program_watermarks() entry to hubbub vtable. Hook it up to
  existing functions that program watermarks.
* Add additional watermark registers.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>