mtd: support ONFI multi lun NAND

mtd: support ONFI multi lun NAND

With onfi a flash is organized into one or more logical units (LUNs).
A" logical unit (LUN) is the minimum unit that can independently execute
commands and report status.

Mtd does not exploit LUN, so make it see a big single flash where size is
lun_size * number_of_lun.

Without this patch MT29F8G08ADBDAH4 size is 512MiB instead of 1GiB.

Artem: split long line on 2 shorter ones.

Signed-off-by: Matthieu Castet <matthieu.castet@parrot.com>
Acked-by: Florian Fainelli <ffainelli@freebox.fr>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Huang Shijie <b32955@freescale.com>