anv: only resort to sync fds internally with no syncobj support

anv: only resort to sync fds internally with no syncobj support

We can rely on only one kind of synchronization object (drm-syncobj)
when it is available. This reduces the number of file descriptors we
use in our implementation.

This will be required later for timeline semaphores implementation, at
this point we won't ever want to use anything else but syncobjs.

v2: Only use has_syncobj for semaphores (Jason)

v3: Only has_syncobj in assert on semaphores in QueueSubmit (Jason)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>