Correctly wait in the fragment stage until all semaphores are signaled

Correctly wait in the fragment stage until all semaphores are signaled

This fixes two issues:
- a crash if the application uses more than one semaphore for presenting because the driver expects one stage per semaphore
- the swapchain image could be not ready yet if the semaphores aren't signaled, #946 is possible related

Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3718>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3718>