85xx: Add P2020DS support

The patch adds support for P2020DS reference platform.
DDR3 interface uses hard-coded initialization rather than SPD
for now and was tested at 667Mhz. Some PIXIS register
definitions and associated code sections need to be fixed.
TSEC1/2/3, NOR flash, MAC/SYS ID EEPROM, PCIE1/2/3 are all
tested under u-boot.

Signed-off-by: Srikanth Srinivasan <srikanth.srinivasan@freescale.com>
Signed-off-by: Travis Wheatley <Travis.Wheatley@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>