rpi5: add initial memory map for bcm2712

This includes:
* 1GB of RAM (from 4GB or 8GB total)
* AXI ranges (main peripherals)

When HDMI cable is plugged in at boot time firmware will
insert "simple-framebuffer" device into devicetree and will
shrink first memory region to 0x3f800000UL. Board setup then
will properly reserve framebuffer region.

When no HDMI cable is plugged in the size of the region will
be 0x3fc00000UL.

Signed-off-by: Dmitry Malkin <dmitry@bedrocksystems.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>