v3dv: expose support for semaphore imports
This was waiting for multisync support in the v3d kernel, which is already available. Exposing this feature however enabled a few more CTS tests that exposed pre-existing bugs in the user-space driver so we fix those here before exposing the feature.
Tested with a multisync kernel using:
dEQP-VK.api.external.*
dEQP-VK.synchronization.*