DRI3 fixes

[Chris Wilson]

There is an issue with the DRI3 protocol that limits stride to CARD16.
Even on old Intel hw we can exceed that which prevents the protocol from
transporting many valid buffers.

[PATCH 1/3] xfree86: Report DRI3 as a built-in module
[PATCH 2/3] sync: Serialise access to the fence before waking clients
[PATCH 3/3] sync: Record the associated Drawable for a shm/fd fence

The first two patches are simple bug fixes, with the last being a major
efficiency burden in the current API.
-Chris