arm64: dts: Add BCM4908 generic board dts

Add generic bare bone bcm94908.dts file to support any 4908 based
design. It supports cpu subsystem, memory and an uart console. This can
be useful for board bring-up and cpu subsystem and memory related kernel
test as well.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20220803175455.47638-6-william.zhang@broadcom.com


Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>