drm/panel: panel-edp: Implement .get_orientation callback

To return the orientation property to drm/kms driver.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
[dianders: fixed space vs. tab indentation]
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220609072722.3488207-4-hsinyi@chromium.org