22.3.5 SetMode() Implementation
SetMode()function is used to select which of the supported output modes the upper layer wishes to use. The choice should be verified to be a supportable mode and then the selected mode should be made the currently active output mode. After this done (and success is guaranteed) update the
Mode->Modevariable with the new currently active mode.
Note: All devices that support the Simple Text Output Protocol must minimally support an 80 x 25 character mode. Additional modes are optional.