mtd: rawnand: use wrappers to call onfi GET/SET_FEATURES

Prepare the fact that some features managed by GET/SET_FEATURES could be
overloaded by vendor code. To handle this logic, use new wrappers
instead of directly call the ->get/set_features() hooks.

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