mesa: Validate sampler settings using uniform storage

mesa: Validate sampler settings using uniform storage

Rather than looking at the settings in individual assembly programs,
look at the settings in the top-level uniform values.  The old code
was flawed because examining each shader stage in isolation could
allow inconsitent usage across stages (e.g., bind unit 0 to a
sampler2D in the vertex shader and sampler1DShadow in the fragment
shader).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>