arm64: dts: imx8mq-librem5: describe power supply for cameras

CAMERA_PWR_EN controls two different power supplies that cameras will use.
The hardware killswitch controls a third one. Describe that appropriately.

The pinctrl that describes the gpio that is used in 2 places here is added
to the pmic. This is done because pmic is powered early enough to make
sure this will work.

When we would have put the same pinctrl property into the 2 regulator nodes
(instead of the pmic), we'd get:

imx8mq-pinctrl 30330000.pinctrl: pin MX8MQ_IOMUXC_GPIO1_IO00 already requested by regulator-csi-1v8; cannot claim for regulator-vcam-2v8
imx8mq-pinctrl 30330000.pinctrl: pin-10 (regulator-vcam-2v8) status -22
imx8mq-pinctrl 30330000.pinctrl: could not request pin 10 (MX8MQ_IOMUXC_GPIO1_IO00) from group camerapwrgrp  on device 30330000.pinctrl

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>