drm/exynos: restore parallel output interface support

The patch adds parallel output interface to FIMD device driver.
It also restores support for panels initialized by boot loader,
but without proper kernel driver.
Driver uses video interface bindings to find connected panel.
It uses drm_panel interface to interact with the panel.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>