i965: Add a "sampler state index" parameter to update_sampler_state().

i965: Add a "sampler state index" parameter to update_sampler_state().

This represents the index into the sampler state table or sampler
default color table (the two are identical).

Right now, this is still the texture unit, but that will change shortly.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>