mtd: rawnand: sunxi: Handle the tREA > tRC / 2 case

In non-EDO, tREA should be less than tRP to guarantee that the
controller does not sample the IO lines too early. Unfortunately, the
sunxi NAND controller does not allow us to have different values for
tRP and tREH (tRP = tREH = tRW / 2).

We have 2 options to overcome this limitation:

1/ Extend tRC to fulfil the tREA <= tRC / 2 constraint
2/ Use EDO mode (only works if timings->tRLOH > 0)

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>