OF: MTD: make plat_nand loadable from DT

This patch sets the of_match_table field inside plat_nand's platform_driver.
We also add a struct mtd_part_parser_data pointer to make sure of_part parsing
works.

If an arch wants to support plat_nand via DT it needs to setup the
platform_nand_data and hook it into the platform_device.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>