i965: Introduce a function to emit a SAMPLER_STATE structure.

i965: Introduce a function to emit a SAMPLER_STATE structure.

This simply assembles all the SAMPLER_STATE fields into their proper bit
locations.  Making it work on all generations was easy enough; some of
the fields are even in the same place.

Not used by anything yet, but will be soon.  I made it non-static so
BLORP can use it too.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>