[Mesa-dev] More pieces for xbgr2101010/abgr2101010 support.

[Mario Kleiner]

These are needed together with Daniel Stone's 10 bpc bgr patches
to make nouveau's 10 bpc support more complete.

All tested on nouveau on a nv96 as primary/display gpu and also
with a radeon as prime renderoffload gpu, and then the other way
round with radeon primary + nouveau renderoffload. Also tested
under X11 DRI2 and DRI3/Present, GLX and EGL, composited and
unredirected. And with Waylands weston normal and with prime
renderoffload.

Patch 1 completes Daniels patches. Patch 2 makes weston work
on nouveau with gbm-format=xbgr2101010, and enables x11 compositing
of depth 30 drawables. Patch 3 makes sure we get the right colors
when compositing on x11 + EGL.

Some patches on top of weston master to test gbm-format=xbgr2101010
are here: https://github.com/kleinerm/weston/tree/westonnew10bpc

-mario