[MTD] Add reboot notifier to Intel NOR flash driver

to make sure the flash is in array mode whenever we're about to
reboot. This is especially useful to allow "soft" reboot to work
which consists of branching back into the bootloader.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>