v3dv: handle empty set layouts

Fixes:
dEQP-VK.api.object_management.max_concurrent.descriptor_set_layout_empty
dEQP-VK.api.object_management.single_alloc_callbacks.descriptor_set_layout_empty

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
1 file changed