ARM: dts: imx7-colibri: add Carrier Board 3.3V/5V regulators

Model the Carrier Board power distribution by adding a fixed 3.3V
and 5V regulator. The 3.3V regulator is connected to the backlight
as well as the display supply. The 5V regulator is used to supply
USB VBUS.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>