mpc83xx: Add the support for MPC8315ERDB board

The features list:
- Boot from NOR Flash
- DDR2 266MHz hardcoded configuration
- Local bus NOR Flash R/W operation
- I2C, UART, MII and RTC
- eTSEC0/1 support
- PCI host

Signed-off-by: Dave Liu <daveliu@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>