mesa/sso: Add pipeline container/state

mesa/sso: Add pipeline container/state

V1:
* Extend gl_shader_state as pipeline object state
* Add a new container gl_pipeline_shader_state that contains
   binding point of the previous object
* Update mesa init/free shader state due to the extension of
   the attibute
* Add an init/free pipeline function for the context

V2:
* Rename gl_shader_state to gl_pipeline_object
* Rename Pipeline.PipelineObj to Pipeline.Current
* Formatting improvement

V3 (idr):
* Split out from previous uber patch.
* Remove '#if 0' debug printfs.

V4 (idr):
* Fix some errors in comments.  Suggested by Jordan.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>