mtd/maps: gpio-addr-flash: new driver for GPIO assisted flash addressing

This driver lets people use GPIO's for additional address lines in case
their processor does not have enough address lines already.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>