dts: vt8500: Update devicetree files for NAND controller on WM8750

Add a NAND flash controller node to the WM8750 soc file, and
add the partition information to the APC8750 board file.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
mtd: vt8500: Add support for WonderMedia WM8xxx-series NAND Flash controller

This patch adds initial support for the NAND flash controller found on
WonderMedia WM8xxx-series (PRIZM) SoCs.

Supports reading partitioning info from devicetree board files.

Tested on VIA APC8750.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>