glsl: Relax qualifier ordering restriction in ES 3.1.

glsl: Relax qualifier ordering restriction in ES 3.1.

... and allow the "binding" qualifier in ES 3.1 as well.

GLSL ES 3.1 incorporates only a few features from the extension
ARB_shading_language_420pack: the relaxed qualifier ordering
requirements and the binding qualifier.

Cc: "11.1" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>