staging: wilc1000: use descriptor-based interface for GPIO

Now making use of descriptor-based interface instead of integer-based
interface for IRQ GPIO.
Added device tree binding reference for WILC SDIO and SPI interface
module. Also moved the code to free gpio descriptor in module remove
as the reference was fetched in probe function.
Updated the TODO file

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>