intel/fs: Do the grf127 hack on SIMD8 instructions in SIMD16 mode

Previously, we only applied the fix to shaders with a dispatch mode of
SIMD8 but the code it relies on for SIMD16 mode only applies to SIMD16
instructions.  If you have a SIMD8 instruction in a SIMD16 shader,
neither would trigger and the restriction could still be hit.

Fixes: 232ed898 "i965/fs: Register allocator shoudn't use grf127..."
Reviewed-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit b4f0d062)