[ARM] 3859/1: Fix devicemaps_init() XIP_KERNEL odd 1MiB XIP_PHYS_ADDR translation error

The ARM XIP_KERNEL map created in devicemaps_init() is wrong.
The map.pfn is rounded down to an even 1MiB section boundary
which results in va/pa translations errors when XIP_PHYS_ADDR
starts on an odd 1MiB boundary and this causes the kernel to
hang.  This patch fixes ARM XIP_KERNEL translation errors for
the odd 1MiB XIP_PHYS_ADDR boundary case.

Signed-off-by: George G. Davis <gdavis@mvista.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>