meta: Add sampler object to texture decompression

meta: Add sampler object to texture decompression

Sampler objects can be used to shadow texture object state without
modifying original application state. Decompression path feels a bit
like path where caching shouldn't happen. But as everything else is
cached already I decided to cache sampler state too.

Signed-off-by: Pauli Nieminen <pauli.nieminen@linux.intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>