mtd: rawnand: Support enabling NV-DDR through SET_FEATURES

Until now the parameter of the ADDR_TIMING_MODE feature was just the
ONFI timing mode (from 0 to 5) because we were only supporting the SDR
data interface. In the same byte, bits 4 and 5 indicate which data
interface is being configured so use them to set the right mode and also
read them back to ensure the right timing has been setup on the chip's
side.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-17-miquel.raynal@bootlin.com