gpio: Add viperboard gpio driver

This adds the mfd cell to use the gpio a and gpio b part
of the Nano River Technologies viperboard.

Signed-off-by: Lars Poeschel <poeschel@lemonage.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
index cd1e2fe..c75ac08 100644
--- a/drivers/mfd/viperboard.c
+++ b/drivers/mfd/viperboard.c
@@ -38,6 +38,9 @@
 MODULE_DEVICE_TABLE(usb, vprbrd_table);
 
 static struct mfd_cell vprbrd_devs[] = {
+	{
+		.name = "viperboard-gpio",
+	},
 };
 
 static int vprbrd_probe(struct usb_interface *interface,