Add the AR934x NAND flash controller register definitions.

Obtained from:	OpenWRT
Extend the Atheros SoC support to include a method to enable/disable
the NAND flash controller.

Add the AR934x NAND flash controller reset routines.
(It's different on subsequent SoCs.)

Tested:

* AR9344, Atheros DB120 reference platform

Obtained from:	OpenWRT