[MTD] [NAND] GPIO NAND flash driver

The patch adds support for NAND flashes connected to GPIOs.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>