board/freescale/mxs: specify the volume-label for vfat

Currently the volume-label for the vfat partition is a string with
the following pattern: 5934-861D.

Specify the volume-label as "boot" to make it easier to identify it.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/freescale/common/mxs/genimage.cfg.template

@@ -8,6 +8,7 @@
 
 image boot.vfat {
 	vfat {
+		label = "boot"
 		files = {
 			%FILES%
 		}