MTD: Nand: Add JZ4740 NAND driver

Add support for the NAND controller on JZ4740 SoCs.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linux-mtd@lists.infradead.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1470/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>