DTS references and debug notes for GPIO pca9548

DTS references and debug notes

https://packages.debian.org/buster/device-tree-compiler

https://github.com/raspberrypi/firmware/tree/master/boot/overlays

https://github.com/raspberrypi/documentation/blob/master/configuration/device-tree.md

https://github.com/raspberrypi/linux/blob/rpi-5.4.y/arch/arm/boot/dts/overlays/i2c-rtc-gpio-overlay.dts

https://github.com/raspberrypi/documentation/blob/master/configuration/device-tree.md#part-4-troubleshooting-and-pro-tips

sudo vcdbg log msg

https://www.raspberrypi.org/documentation/configuration/device-tree.md

https://www.raspberrypi.org/forums/viewtopic.php?t=192580