drm/bridge: lt8912b: Add hot plug detection

Enable hot plug detection when it is available on the HDMI port.
Without this connecting to a different monitor with incompatible timing
before the 10 seconds poll period will lead to a broken display output.

Fixes: 30e2ae94 ("drm/bridge: Introduce LT8912B DSI to HDMI bridge")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Adrien Grassein <adrien.grassein@gmail.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221128112320.25708-1-francesco@dolcini.it