drm/bridge: Add ChromeOS EC ANX7688 bridge driver support

This driver adds support for the ChromeOS EC ANX7688 HDMI to DP converter

For our use case, the only reason the Linux kernel driver is necessary is
to reject resolutions that require more bandwidth than what is available
on the DP side. DP bandwidth and lane count are reported by the bridge via
2 registers and, as far as we know, only chips that have a firmware
version greater than 0.85 support these two registers.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
[The driver is OF only so should depends on CONFIG_OF]
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
[convert to i2c driver, rename to cros_ec_anx7688, add err checks]
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210518141927.24795-3-dafna.hirschfeld@collabora.com