drm/amd/display: Add PPS immediate update flag for DCN2

[Why]
This change is needed for DCN2 to make use of the immediate_update
flag. With this flag, update to PPS will be immediate, rather than
always taking place on dig_update signal.

[How]
Set AFMT_GENERIC7_FRAME/IMMEDIATE_UPDATE bits depending on flag
value.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Ilya <Ilya.Bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>