Just to add to this, I also have an MSI tomahawk b350 and it won't let me overclock in the bios also.
I've just gotten used to running the Ryzen Master program at start and it sets the the top to 3.7 ghz @ stock voltages. I can run that all day and it doesn't hit above 50c in almost every game/application I run.
It is a little frustrating that it doesn't allow me to overclock in the bios, I'm hoping that it is just a bug in the bios and will be updated soon.