package/gd: Add dependency to libvpx

Needed to get reproducable builds and to reproduce this build error:
http://autobuild.buildroot.net/results/046/046dd505feb5e92bdee3d0993366be162da1223a/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gd/gd.mk

@@ -51,6 +51,13 @@ else
 GD_CONF_OPTS += --without-png
 endif
 
+ifeq ($(BR2_PACKAGE_LIBVPX),y)
+GD_DEPENDENCIES += libvpx
+GD_CONF_OPTS += --with-vpx
+else
+GD_CONF_OPTS += --without-vpx
+endif
+
 ifeq ($(BR2_PACKAGE_TIFF),y)
 GD_DEPENDENCIES += tiff
 GD_CONF_OPTS += --with-tiff