glsl: Add validation for the "binding" qualifier.

glsl: Add validation for the "binding" qualifier.

The "binding" qualifier only applies to UBO blocks and samplers, along
with arrays of those types.  (It would also apply to images and atomic
counters, but we don't support those yet.)

This also validates sampler bindings against the maximum number of
texture units, and UBO bindings against the number of uniform buffer
binding points.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>