glsl: enable binding layout qualifier usage for shader storage buffer objects

glsl: enable binding layout qualifier usage for shader storage buffer objects

See GLSL 4.30 spec, section 4.4.5 "Uniform and Shader Storage Block
Layout Qualifiers".

v2:
- Add whitespace in an error message. Delete period '.' at the end of that
error message (Jordan).

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>