st/mesa: run st_nir_lower_tex_src_plane for lowered xyuv/ayuv

Has the effect of removing the nir_tex_src_plane for these formats too.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Marge Bot <mesa/mesa!1896>
Part-of: <mesa/mesa!1896>