imx: mx7: DDR controller configuration for the i.MX7 architecture

The configuration files imximage.cfg are used for the DDR controller
configuration.
Add DDR configuration function to replace the DDR controller
configuration in the imximage.cfg file. The function can be used for
DDR size detection.

Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>