Google has steadfastly refused to add a reboot option to the power menu in stock Android over the years. In fact, it removed everything other than “power off” from that menu in Lollipop. Users have been asking for a reboot option forever, and now Sony is asking for it too. Sony has opened a bug tracker issue and submitted a patch to add it, but Google does not appear to be biting.
Sony Is Trying To Push A Power Menu Restart Option To AOSP As A Developer Setting was written by the awesome team at Android Police.
Source: Andriod Police