MPC83xx: add config options for memory setup.

CPO value and driver strength settings are board specifc.
Also allow SPD data fetch from any accessible I2C EEPROM.

Signed-off-by: Andre Schwarz <andre.schwarz@matrix-vision.de>
Acked-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>