powerpc/85xx: Add P2020DS board support

The P2020 is a dual e500v2 core based SOC with:
* 3 PCIe controllers
* 2 General purpose DMA controllers
* 2 sRIO controllers
* 3 eTSECS
* USB 2.0
* SDHC
* SPI, I2C, DUART
* enhanced localbus
* and optional Security (P2020E) security w/XOR acceleration

The p2020 DS reference board is pretty similar to the existing MPC85xx
DS boards and has a ULI 1575 connected on one of the PCIe controllers.

Signed-off-by: Ted Peters <Ted.Peters@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>