powerpc/mpc83xx: Support for MPC8308 P1M board

This patch adds support for MPC8308 P1M board.
Supported devices:
 DUART
 Dual Ethernet
 NOR flash
 Both I2C controllers
 USB in peripheral mode
 PCI Express

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>