mtd: nand: Add mvebu (PXA / AXP / A38x) NAND device driver

Cloned from the Linux driver v4.2.0-rc2. Plus some patches from
Antoine Tenart enabling controller initialization and ONFI timing
support:

http://lists.infradead.org/pipermail/linux-mtd/2015-July/060197.html

Please note that this driver needs the Linux NAND subsystem sync to v4.1
from Scott to be applied:

https://www.mail-archive.com/u-boot@lists.denx.de/msg175762.html

Otherwise it will not compile.

Tested on the Marvell Armada XP DB-MV784MP-GP eval board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Antoine Tenart <antoine.tenart@free-electrons.com>
Cc: Ezeguil Garcia <ezequiel.garcia@free-electrons.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Scott Wood <scottwood@freescale.com>