mpc85xx: Add support for the supplement configuration unit register

The supplement configuration unit (SCFG) provides chip-specific
configuration and status registers for the device. It is the chip
defined module for extending the device configuration unit (DCFG)
module. It provides a set of CCSR registers in addition to those
available in the device configuration unit.
The base address for this unit is 0x0F_C000.

Signed-off-by: Tang Yuantian <Yuantian.Tang@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>