i965/hsw: Initialize SLM index in state register

i965/hsw: Initialize SLM index in state register

For Haswell, we need to initialize the SLM index in the state
register. This can be copied out of the CS header dword 0.

v2:
 * Use UW move to avoid changing upper 16-bits of sr0.1 (mattst88)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94081
Fixes: piglit arb_compute_shader/execution/shared-atomics.shader_test
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: "11.2" <mesa-stable@lists.freedesktop.org>
Tested-by: Ilia Mirkin <imirkin@alum.mit.edu> (v1)
Reviewed-by: Matt Turner <mattst88@gmail.com>