mesa/sso: Add _mesa_sampler_uniforms_pipeline_are_valid

mesa/sso: Add _mesa_sampler_uniforms_pipeline_are_valid

This is much like _mesa_sampler_uniforms_are_valid, but it operates
across an entire pipeline object.

This function differs from _mesa_sampler_uniforms_are_valid in that it
directly creates the gl_pipeline_object::InfoLog instead of writing to
some temporary buffer.

This was originally included in another patch, but it was split out by
Ian Romanick.

v2 (idr): Fix the loop bounds.  shProg isn't an array, so
ARRAY_SIZE(shProg) was 1, so only the vertex program was validated.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>