[POWERPC] Add bootwrapper support for Motorola PrPMC2800 platform

The Motorola PrPMC280 and PrPMC2800 processor modules sit on an F101 or
PrPMC2800 baseboard, respectively.  There are several variants of each
type of processor module which can have different amounts of memory,
amounts of FLASH, cpu frequencies, and an mv64360 or an mv64362.

The bootwrapper code for that platform reads VPD from an I2C EEPROM
to determine the processor module variant.  From the variant, the
amount of memory, etc. is determined and the device tree is updated
accordingly.  If the variant cannot be determined (e.g., corrupted
VPD or a previously unknown variant), the property values already
in the device tree are used.

Also, the firmware for those platforms does not completely configure
the mv64x60 host bridge so that configuration is done here.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>