[ARM] 4768/2: ixp4xx: Button and LED updates for the nas100d board

 * Convert GPIO and IRQ handling to use the <asm/gpio.h> api.
 * Perform the reset only after the power button has been held down
   for at least two seconds.  Do the reset on the release of the power
   button, so that NAS devices which have been set to auto-power-on (by
   solder bridging the power button) do not continuously power cycle.
 * Remove all superflous constants from nas100d.h
 * Add LED constants to nas100d.h while we're there.
 * Update the board LED setup code to use those constants.

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>