imx6: wandboard: allow booting from MMC 2

One of the SD-CARD slots on the Wandboard Quad B1 is MMC 2. Enable it as a
boot device.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/include/configs/wandboard.h b/include/configs/wandboard.h
index 2e6262f..bdcd5e9 100644
--- a/include/configs/wandboard.h
+++ b/include/configs/wandboard.h
@@ -110,6 +110,7 @@
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \
 	func(MMC, mmc, 1) \
+	func(MMC, mmc, 2) \
 	func(SATA, sata, 0) \
 	func(USB, usb, 0) \
 	func(PXE, pxe, na) \