imx: ventana: switch to SPL

imx: ventana: switch to SPL

Switch to an SPL image. The SPL for Ventana does the following:
 - setup i2c and read the factory programmed EEPROM to obtain DRAM config
   and model for board-specific calibration data
 - configure DRAM per CPU/size/layout/devices/calibration
 - load u-boot.img from NAND and jump to it

This allows for a single SPL+u-boot.img to replace the previous multiple boa
configurations.

Cc: Stefan Roese <[email protected]>
Cc: Otavio Salvador <[email protected]>
Cc: Andy Ng <[email protected]>
Cc: Eric Nelson <[email protected]>
Cc: Tapani Utriainen <[email protected]>
Cc: Tom Rini <[email protected]>
Signed-off-by: Tim Harvey <[email protected]>