vulkan/wsi/x11: add driconf option to not wait under Xwayland

vulkan/wsi/x11: add driconf option to not wait under Xwayland

By default, Mesa's X11 Vulkan WSI will wait for buffers to be ready
before submitting them to Xwayland when the swapchain is created
with the IMMEDIATE mode.

This is undesirable when the Wayland compositor already monitors
fences. A Wayland compositor may want to know the delay between
the buffer submition and the end of the GPU work, this is impossible
to measure if the WSI waits for the buffer to be ready before
submission.

Since most compositors don't monitor fences, let's introduce a driconf
option for this for now. We can reconsider once more compositors
have better support for fences.

Signed-off-by: Simon Ser <contact@emersion.fr>
Acked-by: Michel Dänzer <mdaenzer@redhat.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11290>