draw: make sure pipeline is revalidated when sampler views or samplers change.

draw: make sure pipeline is revalidated when sampler views or samplers change.

Since with llvm execution parts of sampler view and sampler state is baked into
the shader, we need to revalidate otherwise the wrong shader might get used.
(Not completely sure but I think this would not be required for non-llvm case,
along with everything else in these functions.)
This caused bugs in piglit arb_texture_buffer_object-formats, because we never
noticed that the view format changed.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>