Add 'vfat' flag when building kernel with initramfs

We are about to separate VFAT support from 'initramfs' flag. Let's add
'vfat' flag first so that when this happens nothing gets broken.

BUG=chrome-os-partner:9805
TEST=Build success. Factory install shim still works.

Change-Id: Ia432e3b1a6186f4f7c817a1283c86066ced5fef1
Reviewed-on: https://gerrit.chromium.org/gerrit/23193
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Commit-Ready: Vic Yang <victoryang@chromium.org>
Tested-by: Vic Yang <victoryang@chromium.org>
diff --git a/build_image b/build_image
index 3b67a9e..32fcccc 100755
--- a/build_image
+++ b/build_image
@@ -150,7 +150,7 @@
   # network, so we don't require initramfs, but we do require fbconsole to fix
   # a display driver bug.
   if [ "${ARCH}" = "x86" -o "${ARCH}" = "amd64" ] ; then
-    export USE="${USE} initramfs"
+    export USE="${USE} initramfs vfat"
   fi
   # CONFIG_BLK_DEV_RAM is disabled by default.
   # But tftp install needs it to mount rootfs in ram
diff --git a/mod_image_for_recovery.sh b/mod_image_for_recovery.sh
index fd6c74c..10df9a9 100755
--- a/mod_image_for_recovery.sh
+++ b/mod_image_for_recovery.sh
@@ -399,7 +399,7 @@
 
 # Build the recovery kernel.
 FACTORY_ROOT="${BOARD_ROOT}/factory-root"
-USE="fbconsole initramfs" emerge_custom_kernel "$FACTORY_ROOT" ||
+USE="fbconsole initramfs vfat" emerge_custom_kernel "$FACTORY_ROOT" ||
   failboat "Cannot emerge custom kernel"
 
 if [ -z "$FLAGS_kernel_image" ]; then