auxiliary/vl: rename vl_screen_create to vl_dri2_screen_create

auxiliary/vl: rename vl_screen_create to vl_dri2_screen_create

In a preparation of having proper multi-platform/backend handling in VL.

With follow up commits we'll introduce a dispatch within vl_screen
similar to the one in pipe_screen. This way any VL state-tracker can
operate seamlessly, considering the backend/platform is properly setup.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>