ARM: dts: bcm283x-rpi: Move Wifi/BT into separate dtsi

A Wifi/BT chip is quite common for the Raspberry Pi boards. So move those
definitions into a separate dtsi in order to avoid copy & paste. This
change was inspired by a vendor tree patch from Phil Elwell.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://lore.kernel.org/r/1628334401-6577-7-git-send-email-stefan.wahren@i2se.com


Signed-off-by: Nicolas Saenz Julienne <nsaenz@kernel.org>