More displayPort_t, CANVAS as new feature, multi-display cycling

- Further touch-ups with displayPort_t handling.
- CANVAS is a FEATURE now.
- Device specific xxxCmsInit() are registered by device’s init, and
called by CMS upon entry to menu.
- Multiple display devices can be cycled by entering menu invocation
command while in menu.
- The menu invocation command is (was) changed to THR-Mid + YAW-Left +
Pitch-Full to avoid collision with MWOSD menu invocation command.
- More separation attempt.

src/main/io/cms.h

@@ -21,9 +21,15 @@ typedef struct displayPort_s {
     bool cleared;
 } displayPort_t;
 
+// Device management
+typedef void (*cmsDeviceInitFuncPtr)(displayPort_t *);
+bool cmsDeviceRegister(cmsDeviceInitFuncPtr);
+
+// For main.c and scheduler
 void cmsInit(void);
 void cmsHandler(uint32_t);
 
+
 #if 0
 void cmsOpenMenu();
 void cmsUpdate(uint32_t);