mesa: Implement a new GL_MESA_tile_raster_order extension.

The intent is to use this extension on vc4 to allow X11 to do overlapping
CopyArea() within a pixmap without first blitting the pixmap to a
temporary.  With associated glamor patches, improves x11perf
-copywinwin100 performance on a Raspberry Pi 3 from ~4700/sec to
~5130/sec, and is an even larger boost to uncomposited window movement
performance (most copywinwin100 copies don't overlap).

v2: Fix glIsEnabled() on the new enums.
v3: Drop the local spec since I'm upstreaming the spec.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/mesa/state_tracker/st_context.c

@@ -489,6 +489,7 @@ static void st_init_driver_flags(struct st_context *st)
 
    f->NewArray = ST_NEW_VERTEX_ARRAYS;
    f->NewRasterizerDiscard = ST_NEW_RASTERIZER;
+   f->NewTileRasterOrder = ST_NEW_RASTERIZER;
    f->NewUniformBuffer = ST_NEW_UNIFORM_BUFFER;
    f->NewDefaultTessLevels = ST_NEW_TESS_STATE;