drm/amd/display: make aux defer delay and aux sw start delay seperate

[why]
1. defer delay and sw start delay has been mixed up, defer delay was
programmed to AUX_SW_CONTROL:AUX_SW_START_DELAY.
2. There's no delay for defer

[how]
1. Set  aux sw start to 0
2. Add delay for defer scenario

Signed-off-by: Xiaodong Yan <Xiaodong.Yan@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>