regulator: Add DT bindings for RaspberryPi 7" display ATTINY88-based regulator/backlight controller

Add DT bindings for RaspberryPi 7" display ATTINY88-based
regulator/backlight controller, this one is used in the
Raspberry Pi 7" touchscreen display unit.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eric Anholt <eric@anholt.net>
Cc: Mark Brown <broonie@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: devicetree@vger.kernel.org
To: dri-devel@lists.freedesktop.org
Link: https://lore.kernel.org/r/20200809105938.6388-1-marex@denx.de


Signed-off-by: Mark Brown <broonie@kernel.org>