i965/nir/vec4: Implement the dot product operation
i965/nir/vec4: Implement the dot product operation

Adds NIR ALU operations:
   * nir_op_fdot2
   * nir_op_fdot3
   * nir_op_fdot4

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler