mtd: nand: pxa3xx: Add support for the Marvell AC5 SoC

The NAND flash controller (NFC) on the AC5/AC5X SoC is the same as
the NFC used on other Marvell SoCs. It does have the additional
restriction of only supporting SDR timing modes up to 3.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>