qemu-ppce500: Add support for 64bit CCSR map

QEMU 2.3 changes the address layout of the CCSR map in the PV ppce500 machine
to reside in higher address space.

Unfortunately, this exposed a glitch in u-boot for ppce500: While providing
a function to dynamically evaluate the CCSR region's position in physical
address space, we never used it. Plus we forgot to support 64bit physical
addresses.

This patch fixes that mishap, making u-boot work fine with latest QEMU again.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Scott Wood <scottwood@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>