i965/nir/vec4: Add implementation of nir_emit_texture()
i965/nir/vec4: Add implementation of nir_emit_texture()

Uses the nir structure to get all the info needed (sources,
dest reg, etc), and then it uses the common
vec4_visitor::emit_texture to emit the final code.

Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler