mtd: spi-nor: Add spi-nor mtd resume handler

Implemented and populated spi-nor mtd PM handlers for resume ops.
spi-nor resume op re-initializes spi-nor flash to its probed
state by calling the newly implemented spi_nor_init() function.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>