package/mesa3d: VDPAU needs x11

package/mesa3d: VDPAU needs x11

Commit c898f95c275a105caacbb31adf92ef94bd4530c4 added support for
Gallium VDPAU state tracker by updating Config.in to add a dependency on
XORG7. However, mesa3d.mk was not updated to reflect this dependency.

XORG7 dependences is already managed under the ifeq
BR2_PACKAGE_MESA3D_OPENGL_GLX block so reuse this block by making ifeq
depends on a new BR2_PACKAGE_MESA3D_NEEDS_X11 hidden option

Fixes:
 - http://autobuild.buildroot.org/results/bbd102d59bbdca35fd1b5401df2790dd197d1e5f

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>