mtd: rawnand: timings: Use default values for tPROG_max and tBERS_max

The ONFI parameter page of a chip might define more fine grained
tPROG_max and tBERS_max. When we do not have this information, we
default to the highest possible values (they are maxima anyway).

There is no point setting these fields at runtime, so explicitly move
these defaults to the main ONFI SDR timings structure. This way, we
will also be able to return a pointer to mode 0 directly when we will
create a default reset configuration.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529111322.7184-18-miquel.raynal@bootlin.com