i965/fs: Add a shader_stats struct.

It'll grow further, and we'd like to avoid adding an additional
parameter to fs_generator() for each new piece of data.

v2 (idr): Rebase on 17 months.  Track a visitor instead of a cfg.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs_visitor.cpp

@@ -952,7 +952,7 @@ fs_visitor::init()
    this->pull_constant_loc = NULL;
    this->push_constant_loc = NULL;
 
-   this->promoted_constants = 0,
+   this->shader_stats.promoted_constants = 0,
 
    this->grf_used = 0;
    this->spilled_any_registers = false;