Add support for DiskOnChip G3 chips. The support is quite
limited yet :
 - no flash writes/erases are implemented
 - ECC fixes are not implemented
 - powerdown is not implemented
 - IPL handling is not yet done

On the brighter side, the chip reading does work.
Signed-off-by: NRobert Jarzmik <robert.jarzmik@free.fr>