ARM: dts: omap3-beagle: Provide NAND ready pin

On these boards NAND ready pin status is avilable over
GPMC_WAIT0 pin.

For NAND we don't use GPMC wait pin monitoring but
get the NAND Ready/Busy# status using GPIOlib.
GPMC driver provides the WAIT0 pin status over GPIOlib.

Read speed increases from 13212 KiB/ to 15753 KiB/s
and write speed was unchanged at 4404 KiB/s.

Measured using mtd_speedtest.ko on omap3-beagle-c4.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>