mtd: onenand: add new option to control initial onenand unlocking

A new option ONENAND_SKIP_INITIAL_UNLOCKING is added. This allows
to disable initial onenand unlocking when the driver is initialized.

Signed-off-by: Roman Tereshonkov <roman.tereshonkov@nokia.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>