package/supertuxkart: needs freetype

package/supertuxkart: needs freetype

https://github.com/supertuxkart/stk-code/blob/master/CMakeLists.txt#L231

Build would fail without this patch using this defconfig:

BR2_x86_64=y
BR2_TOOLCHAIN_BUILDROOT_LOCALE=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_PACKAGE_SUPERTUXKART=y
BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_DRI_DRIVER_I965=y
BR2_PACKAGE_MESA3D_OPENGL_EGL=y
BR2_PACKAGE_XORG7=y

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Romain Naour <romain.naour@gmail.com>
Tested-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>