meson: Move -Dvulkan-drivers handling higher in the file

The window-system auto-detection code (specifically for glx) relies on
with_any_vk being available.  This fixes the Vulkan-only build.  Also,
this puts it up near the handling of -Ddri-drivers and -Dgallium-drivers
which seems to make a bit more sense.

Fixes: 118a7f044191d4ab15ac9 "meson: add support for xlib glx"
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
1 file changed