mtd: nand: ndfc: add multiple chip select support

This patch extends NDFC driver to support all 4 chip selects
available in NDFC NAND controller. Tested on custom 460EX board
with 2 chip select NAND device.

Artem: white-space cleanups

Signed-off-by: Felix Radensky <felix@embedded-sol.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>