rpi5: Use devicetree as alternative way to read IO base addresses

rpi5: Use devicetree as alternative way to read IO base addresses

MBOX and Watchdog on RPi5/bcm2712 have a different base IO offsets.
Find them via devicetree blob passed by bootloader.

Signed-off-by: Dmitry Malkin <dmitry@bedrocksystems.com>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Tested-by: Jens Maus <mail@jens-maus.de>
Tested-by: Darko Alavanja <darko.alavanja@konsulko.com>
Signed-off-by: Ivan T. Ivanov <iivanov@suse.de>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
[backport of the commit 60878e753c3d37ddc974c0de9da643850df175b6 from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I4c674196a08176b649f325cd777c5f01adad1380