intel/fs: Use groups for SIMD16 LINTERP on gen11+

intel/fs: Use groups for SIMD16 LINTERP on gen11+

This is better than compression control because it naturally extends to
SIMD32.

v2:
 - Push/pop instruction state around adjusted codegen (Ken)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>