mpc8308: support for Freescale MPC8308 cpu

This patch adds basic support for Freescale MPC8308 CPU. Serial ports,
NOR flash and integrated Ethernet controllers are supported.
PCI Express is also supported. eSDHC, NAND and USB may work but aren't
tested (using ULPI PHY requires additional patch).

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>