The avcodec module and vaapi vout module share the same VA API connection.
This allowed for a bug when XCloseDisplay() is called first in one module,
when the other still uses the VA API connection. Ommitting XCloseDisplay()
in the module that quits first allows for a resource leak. Therefor the best
solution is to also share the X11 Display connection for VA API.

Note: the VAAPI XCB vout uses another X11/XCB connection for managing its
windows and their events.

This reverts commit 74a2179e.