auxiliary/vl: rework the build of the VL code

auxiliary/vl: rework the build of the VL code

Rather than shoving all the VL code for non-VL targets, increasing
their size, just split it out and use it when needed. This gives us
the side effect of building vl_winsys_dri.c once, dropping a few
automake warnings, and reducing the size of the dri modules as below

   text    data     bss     dec     hex filename
5850573  187549 1977928 8016050  7a50b2 before/nouveau_dri.so
5508486  187100  391240 6086826  5ce0aa after/nouveau_dri.so

The above data is for a nouveau + swrast + kms_swrast 'megadriver'.

v2: Do not include the vl sources in the auxiliary library.
v3: Rebase. Add nine.

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