gallium: Enable ARB_clip_control for gallium drivers.

Gallium should be prepared fine for ARB_clip_control.
So enable this and mention it in the release notes.

v2:
Only enable for drivers announcing the freshly introduced
PIPE_CAP_CLIP_HALFZ capability.

v3:
Use extension enable infrastructure to connect PIPE_CAP_CLIP_HALFZ
with ARB_clip_control.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Mathias Froehlich <Mathias.Froehlich@web.de>
4 files changed