glsl: Count shader inputs and outputs separately

glsl: Count shader inputs and outputs separately

Starting with OpenGL 3.2 input limits and output limits for stages may
not match.  This means they need to be accounted separately.

No piglit regressions.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>