aco: fix init_any_pred_defined() for loop header phis

aco: fix init_any_pred_defined() for loop header phis

This includes setting the correct end point of the propagation and
not propagating the incoming values after the loop header.
This patch also changes the propagation to a single iteration for
loop exit phis.

No fossil-db changes.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
aco: don't propagate incoming value in init_any_pred_defined()

No fossil-db changes.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11659>