drm/imx: parallel-display: switch to drm_panel_bridge

Defer panel handling to drm_panel_bridge, unifying codepaths for the
panel and bridge cases.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Chris Healy <cphealy@gmail.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de> # on imx6q-nitrogen6x
Link: https://patchwork.freedesktop.org/patch/msgid/20240602-drm-imx-cleanup-v3-8-e549e2a43100@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>