nv50/ir: Support vector movs

nv50/ir: Support vector movs

nir_opt_mov and nir_op_vecN are only the same if the mov is only a
single component.  Otherwise the vec loop will try to access src[c]
where c > 0 which breaks for nir_op_mov.  It's uncommon but scalar
back-ends can see vector movs so we need to handle this correctly.

Fixes: 6513c675ad31 ("nv50/ir/nir: implement nir_alu_instr handling")
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: M Henning <drawoc@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24167>