mesa: faster validation of sampler unit mapping for SSO

mesa: faster validation of sampler unit mapping for SSO

Code was inspired from _mesa_update_shader_textures_used

However unlike _mesa_update_shader_textures_used that only check for a single
stage, it will check all stages.

It avoids to loop on all uniforms, only active samplers are checked.

For my use case: high FS frequency switches with few samplers.
Perf event (relative to nouveau_dri.so) goes from 5.01% to 1.68% for
the _mesa_sampler_uniforms_pipeline_are_valid function.

Signed-off-by: Gregory Hainaut <gregory.hainaut@gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>