protocol: add Presentation feedback flags

protocol: add Presentation feedback flags

Add the missing feedback flags to the Presentation extension protocol
specification.

These flags are slightly different from the previous RFCv3.1 definition:
http://lists.freedesktop.org/archives/wayland-devel/2014-March/013598.html

Now, all compositors are safe to use 0 as the flags if they don't bother
setting them properly. 0 is the "worst case" with the least guarantees.

The meaning of ZERO_COPY is not exactly the opposite of the old COPY
flag. ZERO_COPY is more strict, but applies only to that one surface.
Therefore it can be used to verify a zero-copy video playback pipeline,
also to a hardware overlay.

There is no longer a flag to clearly indicate if the final presentation
was done by a copy or a page flip. ZERO_COPY forbids the copy, but VSYNC
alone does allow copy in case it cannot tear.  It is possible to have
first a compositing pass, and then another copy into the frontbuffer,
and still set VSYNC if it cannot tear.  Usually "cannot tear" is too
hard to guarantee with a copy, so it often implies a page flip.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>