arm: bcm2835: Fix FIQ early ioremap

The ioremapping creates mappings within the vmalloc area. The
equivalent early function, create_mapping, now checks that the
requested explicit virtual address is between VMALLOC_START and
VMALLOC_END. As there is no reason to have any correlation between
the physical and virtual addresses, put the required mappings at
VMALLOC_START and above.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>