i965: Use NIR by default for vertex shaders

i965: Use NIR by default for vertex shaders

Shader-db results for vec4 on i965:

   total instructions in shared programs: 1499894 -> 1502261 (0.16%)
   instructions in affected programs:     1414224 -> 1416591 (0.17%)
   helped:                                2434
   HURT:                                  10543
   GAINED:                                1
   LOST:                                  0

Shader-db results for vec4 on g4x:

   total instructions in shared programs: 1437411 -> 1439779 (0.16%)
   instructions in affected programs:     1362402 -> 1364770 (0.17%)
   helped:                                2434
   HURT:                                  10544
   GAINED:                                0
   LOST:                                  0

Shader-db results for vec4 on Iron Lake:

   total instructions in shared programs: 1437214 -> 1439593 (0.17%)
   instructions in affected programs:     1362205 -> 1364584 (0.17%)
   helped:                                2433
   HURT:                                  10544
   GAINED:                                1
   LOST:                                  0

Shader-db results for vec4 on Sandy Bridge:

   total instructions in shared programs: 2022092 -> 1941570 (-3.98%)
   instructions in affected programs:     1886838 -> 1806316 (-4.27%)
   helped:                                7510
   HURT:                                  10737
   GAINED:                                0
   LOST:                                  0

Shader-db results for vec4 on Ivy Bridge:

   total instructions in shared programs: 1853749 -> 1804960 (-2.63%)
   instructions in affected programs:     1686736 -> 1637947 (-2.89%)
   helped:                                6735
   HURT:                                  11101
   GAINED:                                0
   LOST:                                  0

Shader-db results for vec4 on Haswell:

   total instructions in shared programs: 1853749 -> 1804960 (-2.63%)
   instructions in affected programs:     1686736 -> 1637947 (-2.89%)
   helped:                                6735
   HURT:                                  11101
   GAINED:                                0
   LOST:                                  0

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Matt Turner <mattst88@gmail.com>