intel/fs: Move the scalar-region conversion to the generator.

Move the scalar-region conversion from the IR to the generator, so it
doesn't affect the Gen11 path. We need the non-scalar regioning
for a later lowering pass that we are adding.

v2: Better commit message (Matt)

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs_visitor.cpp

@@ -194,7 +194,7 @@ fs_visitor::emit_interpolation_setup_gen4()
     */
    this->wpos_w = vgrf(glsl_type::float_type);
    abld.emit(FS_OPCODE_LINTERP, wpos_w, delta_xy,
-             component(interp_reg(VARYING_SLOT_POS, 3), 0));
+             interp_reg(VARYING_SLOT_POS, 3));
    /* Compute the pixel 1/W value from wpos.w. */
    this->pixel_w = vgrf(glsl_type::float_type);
    abld.emit(SHADER_OPCODE_RCP, this->pixel_w, wpos_w);