i965: Prepare gs_state emitting code to include gen4-5.

i965: Prepare gs_state emitting code to include gen4-5.

Since we always call brw_batch_emit anyways, we can hopefully make things
simpler by calling it only once, and then branching inside its body. This
can be helpful when bringing the gen4-5 code into this function.

Additionally, check for GEN_GEN == 6 instead of < 7 in cases that won't apply
to lower gens.

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>