mtd: rawnand: arasan: Finer grain NV-DDR configuration

Add support for the timings register which may improve a bit the
overall throughput.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210527084959.208804-2-miquel.raynal@bootlin.com