lima: run nir dce after nir_lower_vec_to_movs

lima: run nir dce after nir_lower_vec_to_movs

Some of the 'vec*' nir instructions may hold references to dead code
until the nir_lower_vec_to_movs pass runs.
After nir_lower_vec_to_movs, that code can finally be cleaned by dce,
so add an additional dce pass.
This not only potentially further removes unneeded code from the nir
representation but also prevents bugs with the compiler from special
case unused code that is not expected (e.g. root undef type nodes).

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9507>