mtd: bf5xx_nand: drop no-op PM support

This driver's suspend/resume hooks are no-ops, so just remove them.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mike Frysinger <vapier.adi@gmail.com>