auxiliary/vl: add galliumvl_stub.la

auxiliary/vl: add galliumvl_stub.la

Will be used by the non-VL targets, to stub out the functions called
by the drivers. The entry point to those are within the VL
state-trackers, yet the compiler cannot determine that at link time.
Thus we'll need to stub them out to prevent unresolved symbols in the
dri, egl, gbm and pipe-loader targets.

v2: Rebase.

Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>