drm/amd/display: fix eDP bootup/S4 backlight on

also pass-in correct dispclk tor DMCU

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>