An experimental (hence the 'z' prefix) linux_dmabuf Wayland protocol
extension for creating dmabuf-based wl_buffers in a generic manner.

This does not include proper dmabuf metadata negotiation because
there is no way to communicate all dmabuf constraints from the
compositor to a client before-hand. The client has to create a
wl_buffer wrapping one or more dmabuf buffers and then listen at
the feedback object returned to know if the operation was successful.

RFCv1 changes (after a first draft without code):
- some renames of interfaces and argument, no semantic changes
- added destructor protocol to dmabuf_batch
- added feedback interface for buffer creation

v2 changes:
- use drm_fourcc.h as authoritative source for format codes
- add support for the 64-bit layout qualifier and y-inverted dmabufs
- simplify the 'add' request (no need to preserve fd numerical id)
- add explicit plane index in the 'add' request
- integrate the 'feedback' object events to the batc...