drm/bridge: lt8912b: set hdmi or dvi mode

The Lontium LT8912 does have a setting for DVI or HDMI. This patch reads
from EDID what the display needs and sets it accordingly.

Fixes: 30e2ae94

 ("drm/bridge: Introduce LT8912B DSI to HDMI bridge")
Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Acked-by: Adrien Grassein <adrien.grassein@gmail.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220922124306.34729-3-dev@pschenker.ch