drm/amd/display: fix problems in power_helper

[Why & How]
Fix following problems:
- In abm config, forget to initialize config.ambient_thresholds_lux.
- Adjust the coding style problem
- Restrict to call psr_su_set_dsc_slice_height() under edp only

Reviewed-by: Robin Chen <robin.chen@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>