arm64: dts: broadcom: Add reference to RPi Zero 2 W

This adds a reference to the dts of the Raspberry Pi Zero 2 W,
so we don't need to maintain the content in arm64.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>