Android: move drivers' symlinks to /vendor (v2)

Android: move drivers' symlinks to /vendor (v2)

Having moved gallium_dri.so library to /vendor/lib/dri
also symlinks need to be coherently created using TARGET_OUT_VENDOR instead of TARGET_OUT
or all non Intel drivers will not be loaded with Android N and earlier,
thus causing SurfaceFlinger SIGABRT

(v2) simplification of post install command

Fixes: c3f75d483c ("Android: move libraries to /vendor")
Cc: 17.3 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com> (v1)
Reviewed-by: Rob Herring <robh@kernel.org> (v1)
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>