drm/bridge: add it6505 driver

This adds support for the iTE IT6505.
This device can convert DPI signal to DP output.

From: Allen Chen <allen.chen@ite.com.tw>
Tested-by: Hsin-yi Wang <hsinyi@chromium.org>
Signed-off-by: Hermes Wu <hermes.wu@ite.com.tw>
Signed-off-by: Allen Chen <allen.chen@ite.com.tw>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220114091502.333083-1-allen.chen@ite.com.tw