[why]
dwb was not POR previosly.
now need to enable dwb in dml2.

Limitation:
HW DML assumes only one DWB
one set of watermark for all 4 watermark sets
one stream has one DWB only.
WB scaling dml input has one set of scaling tap.
(no chroma so far)

needs to follow up
Reviewed-by: Chris Park <chris.park@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>