drm/amd/display: Fix VABC Init and OLED Support

drm/amd/display: Fix VABC Init and OLED Support

[Why]
TCONs supporting VESA AUX Backlight does not always
support VESA Smooth Brightness. Driver software
needs to implement smooth brightness by periodically
updating the brightness by small steps. Driver
implementation is completed and verified on LCD
panels but solution is missing for OLED panels.

[How]
Updated driver to include smooth brightness for
OLED panels using VESA Aux Backlight.
Revert original workaround for VABC on oled issue,
as it is no longer needed.
Add VABC backlight Initialization sequence from
driver side.
Add fix to remove conflict between FW and driver
backlight programming for future ASIC.
Enable VABC for all future asic revisions.

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Iswara Nagulendran <Iswara.Nagulendran@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>