mtd: rawnand: jedec: Define the number of parameter pages

Use a macro to define the number of parameter page instead of
hardcoding it everywhere.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200428094302.14624-9-miquel.raynal@bootlin.com