drm/amd/display: Implementing new bandwidth registers for DCE120

Registers are added and defined.
Programmed to default values.
Stutter level watermark register is being set to calculated value.
Urgent level registers are programmed to the same as urgency.
The programming of the registers is not expected to have any
functional difference in performance.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>