drm/amd/display: turn off eDP lcdvdd and backlight if not required

[why]
A+N configuration, eDP on A-APU is off, extended display active.
Resume from s4, eDP's backlight is still on.

[how]
Turn off inactive eDP backlight and lcdvdd.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Jing Zhou <Jing.Zhou@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>