mtd: rawnand: gpmi: support ->setup_data_interface()

Until now the GPMI driver had its own timings logic while the core
already handles that and request the NAND controller drivers to support
the ->setup_data_interface() hook. Implement that hook by reusing the
already existing function. No real glue is necessary between core timing
delays and GPMI registers because the driver already translates the
ONFI timing modes into register values.

Make use of the core's tREA, tRLOH and tRHOH values that allow computing
more precise timings for mode [0-3] and get significantly better values
(+20% with an i.MX6 Sabre Auto board). Otherwise use the existing logic.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>