rpi: Adjust fdt_addr_r to a sane address

Back in the old days, 0x100 was used as the address to pass the device tree
from firmware into the kernel. This has since changed to a more dynamic
location, so using 0x100 actually breaks more things than it helps with.

Let's move the device tree default location for distro boot to a more sane
place that gives us enough head room in low memory.

Reported-by: Tuomas Tynkkynen <tuomas@tuxera.com>
Signed-off-by: Alexander Graf <agraf@suse.de>