NAND: Enable nand lock, unlock feature

Enable nand lock, unlock and status of lock feature.
Not every device and platform requires this, hence,
it is under define for CONFIG_CMD_NAND_LOCK_UNLOCK

Nand unlock and status operate on block boundary instead
of page boundary. Details in:
http://www.micron.com/products/partdetail?part=MT29C2G24MAKLAJG-6%20IT



Intial solution provided by Vikram Pandita <vikram.pandita@ti.com>
Includes preliminary suggestions from Scott Wood

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>