rng: iproc_rng200: Enable support for RPi4 armv7

On the RPi4 armv7 build we have the situationt that we use physical
addresses of 64 bit, while the virtual addresses are 32 bit.
Remap the base address in this scenario via map_physmem().

Signed-off-by: Matthias Brugger <mbrugger@suse.com>