i965: Fix texturing in the vec4 TCS and GS backends.

i965: Fix texturing in the vec4 TCS and GS backends.

We were failing to zero m0.2 of the sampler message header for TCS and
GS messages in the simple case.  fs_generator has done this for about
a year now, but we missed it in vec4_generator.

Fixes ES31-CTS.core.texture_cube_map_array.sampling,
GL45-CTS.texture_cube_map_array.sampling, and many
dEQP-GLES31.functional.shaders.opaque_type_indexing.sampler subtests:
- dynamically_uniform.tessellation_control.isampler3d
- dynamically_uniform.tessellation_control.isamplercube
- dynamically_uniform.tessellation_control.sampler2d
- dynamically_uniform.tessellation_control.usamplercube
- dynamically_uniform.tessellation_control.sampler2darray
- dynamically_uniform.tessellation_control.isampler2darray
- dynamically_uniform.tessellation_control.usampler3d
- dynamically_uniform.tessellation_control.usampler2darray
- dynamically_uniform.tessellation_control.usampler2d
- dynamically_uniform.tessellation_control.sampler3d
- dynamically_uniform.tessellation_control.samplercube
- dynamically_uniform.tessellation_control.isampler2d
- uniform.tessellation_control.isampler3d
- uniform.tessellation_control.isamplercube
- uniform.tessellation_control.usampler2d
- uniform.tessellation_control.usampler3d
- uniform.tessellation_control.sampler2darray
- uniform.tessellation_control.isampler2darray
- uniform.tessellation_control.usampler2darray
- uniform.tessellation_control.sampler2d
- uniform.tessellation_control.usamplercube
- uniform.tessellation_control.sampler3d
- uniform.tessellation_control.samplercube
- uniform.tessellation_control.isampler2d

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>