drm/msm/dp: clear EDID on display unplug

drm/msm/dp: clear EDID on display unplug

Currently the driver only updates the EDID when it detects a connected
monitor, which results in the connector still listing outdated modes
even after the display is unplugged. Set connector's EDID to NULL on
unplug to clear the list of modes.

Tested-by: Val Packett <val@packett.cool> # x1e80100-dell-latitude-7455
Tested-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com> # Hamoa IOT EVK, QCS8300 Ride
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/727619/
Link: https://lore.kernel.org/r/20260524-hpd-refactor-v6-10-cf3ab488dd7b@oss.qualcomm.com