drm/bridge: chrontel-ch7033: Add a new driver

This is a driver for video encoder with VGA and DVI/HDMI outputs.

There is no documentation for the chip -- the operation was guessed from
what was sniffed on a Dell Wyse 3020 ThinOS terminal, the register names
come from the ch7035 driver in Mediatek's GPL code dump.

Only bare minimum is implemented -- no fancy stuff, such as scaling. That
would only worsen our misery. We don't load the firmware and we don't need
to even bother enabling the MCU.  There are probably no distributable
firmware images anyway.

Tested with a handful of monitors ranging from 1024x768@75 to 1400x1050@60,
with VGA as well as DVI.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424213539.93157-4-lkundrak@v3.sk