intel/compiler: Fill a compiler statistics struct

intel/compiler: Fill a compiler statistics struct

This commit is all annoying plumbing work which just adds support for a
new brw_compile_stats struct.  This struct provides a binary driver
readable form of the same statistics we dump out to stderr when we
INTEL_DEBUG is set with a shader stage.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>