configs/beaglebone: Add missing genimage.cfg file

Commit 7d0b7d3c27a6 ("configs/beaglebone: Use genimage
to produce the SD card image") introduce genimage usage,
but forgot to add the genimage config file. Fix it.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/beaglebone/genimage.cfg

@@ -0,0 +1,30 @@
+image boot.vfat {
+	vfat {
+		files = {
+			"MLO",
+			"u-boot.img",
+			"zImage",
+			"uEnv.txt",
+			"am335x-bone.dtb",
+			"am335x-boneblack.dtb"
+		}
+	}
+	size = 16M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot {
+		partition-type = 0xC
+		bootable = "true"
+                image = "boot.vfat"
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+		size = 512M
+	}
+}