mesa/glsl: build list of program resources during linking

mesa/glsl: build list of program resources during linking

Patch adds ProgramResourceList to gl_shader_program structure.
List contains references to active program resources and is
constructed during linking phase.

This list will be used by follow-up patches to implement hooks
for GL_ARB_program_interface_query. It can be also used to
implement any of the older shader program query APIs.

v2: code cleanups + note for SSBO and subroutines (Ilia Mirkin)
v3: code cleanups + assert(MESA_SHADER_STAGES < 8) (Martin Peres)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Martin Peres <martin.peres@linux.intel.com>