This implements version 4 of the linux-dmabuf protocol,
and at the same time, identifies it as stable, since
this is stable upstream. This is required on some new
drivers.

The unstable plugin is kept around to avoid disrupting
systems where this is already in use. It just creates
a version 3 instance of the same code.

[ChangeLog][Plugins] Added support for linux-dmabuf-v1
stable protocol, version 4. To use it, select
"linux-dmabuf-v1" as the client buffer integration.
The old (version 3) implementation can still be used
under the name "linux-dmabuf-unstable-v1" for
compatibility.

Fixes: QTBUG-144800
Change-Id: I49a714b0046f030b88c38905276be7d2b16cef8b
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>