mtd: spinand: Give the bus interface to the configuration helper

mtd: spinand: Give the bus interface to the configuration helper

The chip configuration hook is the one responsible to actually switch
the switch between bus interfaces. It is natural to give it the bus
interface we expect with a new parameter. For now the only value we can
give is SSDR, but this is subject to change in the future, so add a bit
of extra logic in the implementations of this callback to make sure
both the core and the chip driver are aligned on the request.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>