glsl: parser changes for GL_ARB_explicit_uniform_location

glsl: parser changes for GL_ARB_explicit_uniform_location

Patch adds a preprocessor define for the extension and stores explicit
location data for uniforms during AST->HIR conversion. It also sets
layout token to be available when having the extension in place.

v2: change parser check to require GLSL 330 or enabling
    GL_ARB_explicit_attrib_location (Ian)
v3: fix the check and comment in AST->HIR (Petri)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>