wifi: winc1500: Add Device Tree support

Add a dts binding for the Atmel WINC1500 WIFI chip.  Update the
quark_se_c1000_devboard to utilize this binding as well as the wifi
sample app.

We now get all the GPIOs related to the Atmel WINC1500 from the device
tree.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>