Implement picture pool for VAAPI-X11 vout.

Use vlc_va_* wrapper to call vaInitialize and vaTerminate

Initialize/terminate libva only once. VAAPI calls are now being used by
2 modules which only have interaction with each other through vlc core.
Both modules (codec and vout) can be initiated independently they should
not call vaIntialize (or vaTerminate) one after each other (or simultanously).

Add option to select stream_output module to enable an es by default.

Video output VAAPI-X11 (-V vaapi-x11) depends on --ffmpeg-hw to be enabled.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

This fixes the crash when Media Library tries to add "My Videos" / "My
Pictures" / etc. playlist entries to a ML when browsing them through "My
Computer" service discovery.

Signed-off-by: Laurent Aimar <fenrir@videolan.org>

Remove tabs, trailing spaces, and write-only variables

This partially reverts commit add821b0.

Caused by [231a9671]
Sorry for the disturbance

(we might need a PSK box later)

This merges the Linux DVB and Windows BDA backend behind the same
plugin-internal interface.
Like the existing BDA plugin, this does not support PID filters,
signal levels nor DVB-S2.