anv: refcount semaphores

anv: refcount semaphores

Delayed submissions required by timeline semaphores mean we need to be
able to update the sync fd backed semaphores in a delayed fashion.
This could mean a race between the application destroying the
semaphore and the submission code trying to update it with the new
sync fd.

This change prepares semaphores to be refcounted, we'll most likely
only take a reference for cases where we signal a sync fd semaphore.

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