I'll offer, if I may, a simple reductio ad absurdium to the premise of your question. If Jesus had not been crucified, He (in the Person of God) still would have been the creator of the forces that ended His human life. It wouldn't have mattered if He died in a tower accident or disease or even the slow process usually called "Natural Causes". So no matter how Jesus died, calling it suicide, is an immaterial accident.
For the theological reasons why a shedding of blood was necessary for redemption of mankind, I think you ought to ask a question about crucifixion on Christianity.SE, and St. Thomas Aquinas tackles the question of whether Christ needed to suffer in the summa theologiae
For since it is impossible for God's foreknowledge to be deceived and His will or ordinance to be frustrated, then, supposing God's foreknowledge and ordinance regarding Christ's Passion, it was not possible at the same time for Christ not to suffer, and for mankind to be delivered otherwise than by Christ's Passion. And the same holds good of all things foreknown and preordained by God, as was laid down in I:14:13.
And the relevant bit about God's foreknowledge being this
Now God knows all contingent things not only as they are in their causes, but also as each one of them is actually in itself. And although contingent things become actual successively, nevertheless God knows contingent things not successively, as they are in their own being, as we do but simultaneously
The other important thing to remember is that Jesus promised that He would be raised again. So, unlike suicide, which is an end of life. If there was certain foreknowledge of life after death, suicide would be counted as a righteous act of faith which, incidentally, His followers would take upon themselves and He encouraged it:
Then he said to them all: “Whoever wants to be my disciple must deny themselves and take up their cross daily and follow me.