drm/amd/display: refactor ILR to make it work

[ Upstream commit 6ec87647

 ]

[Why]
Current ILR toggle is on/off as a part of panel
config for new function, which breaks original
ILR logic

[How]
Refactor ILR and take panel config into account

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Sherry Wang <yao.wang1@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: d9e86582

 ("drm/amd/display: Simplify brightness initialization")
Signed-off-by: Sasha Levin <sashal@kernel.org>