clearfog: Install mtools for the USB genimage

This is needed by our USB bootable flash. Our EL7 builders might not
have it:

  + genimage --rootpath /scratch/build-clearfog/target --tmppath /scratch/build-clearfog/build/genimage.tmp --inputpath /scratch/build-clearfog/images --outputpath /scratch/build-clearfog/images --config /scratch/czechlight/board/czechlight/clearfog/usb-genimage.cfg
  vfat(usb-flash.vfat): adding file 'usb-boot.scr' as 'boot.scr' ...
  sh: mcopy: command not found
  vfat(usb-flash.vfat): failed to generate usb-flash.vfat
  make[1]: *** [target-post-image] Error 1
  make: *** [_all] Error 2

Change-Id: Ie343819b841d5b5e928eceb16c266422eb7325d6
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index 5172ccc..a89ac86 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -67,5 +67,6 @@
 BR2_TARGET_UBOOT_BOOT_SCRIPT_SOURCE="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/boot.scr.txt"
 BR2_PACKAGE_HOST_DOSFSTOOLS=y
 BR2_PACKAGE_HOST_GENIMAGE=y
+BR2_PACKAGE_HOST_MTOOLS=y
 BR2_PACKAGE_HOST_RAUC=y
 CZECHLIGHT_NETCONF=y