drm/radeon: fix dpms when driver backlight control is disabled
drm/radeon: fix dpms when driver backlight control is disabled

If driver backlight control is disabled, either by driver
parameter or default per-asic setting, revert to the old behavior.

Fixes a regression in commit:
4281f46ef839050d2ef60348f661eb463c21cc2e

Reviewed-by: Michel Dänzer <242b79f0804cf52679d58f27ed754158c1323c75@amd.com>
Signed-off-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs