Go into your control options and assign buttons in the Interface Mode section for Next Panel Tab and Previous Panel Tab. As Robert said, the buttons either side of the hat are probably ideal. If you didn't know, buttons can be assigned to different functions at the same time. For example, when the panels are open the buttons can navigate tabs, and when they are closed they can select targets. The same goes for SRV controls, galaxy map, and etc. There are even flight landing overrides where you can assign them for thrusters.