Revert "drm/amd/display: Only restore backlight after amdgpu_dm_init or dm_resume"

This fix regressed the original issue that commit 7875afaf
("drm/amd/display: Fix brightness level not retained over reboot") solved,
so revert it until a different approach to solve the regression that
it caused with AMD_PRIVATE_COLOR is found.

Fixes: a490c8d7 ("drm/amd/display: Only restore backlight after amdgpu_dm_init or dm_resume")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4620


Cc: stable@vger.kernel.org
Signed-off-by: Matthew Schwartz <matthew.schwartz@linux.dev>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>