Add DFU runtime and mode "class"

With the runtime and mode portions in separate classes, a single
application should only be building with one or the other enabled.  In
some applications both might be desired at build time.

The CFG_TUD_DFU_RUNTIME_AND_MODE option creates a DFU class, which asks
the application which mode to initialize to.  This allows a runtime
change between RT and DFU mode, by just reinitializing tusb.

src/tusb_option.h

@@ -241,6 +241,10 @@
   #define CFG_TUD_DFU_MODE        0
 #endif
 
+#ifndef CFG_TUD_DFU_RUNTIME_AND_MODE
+  #define CFG_TUD_DFU_RUNTIME_AND_MODE      0
+#endif
+
 #ifndef CFG_TUD_DFU_TRANSFER_BUFFER_SIZE
   #define CFG_TUD_DFU_TRANSFER_BUFFER_SIZE  64
 #endif
@@ -285,6 +289,12 @@
   #error Control Endpoint Max Packet Size cannot be larger than 64
 #endif
 
+#if (CFG_TUD_DFU_RUNTIME_AND_MODE && CFG_TUD_DFU_RUNTIME) \
+    || (CFG_TUD_DFU_RUNTIME_AND_MODE && CFG_TUD_DFU_MODE) \
+    || (CFG_TUD_DFU_RUNTIME && CFG_TUD_DFU_MODE)
+    #error Only one of CFG_TUD_DFU_RUNTIME_AND_MODE, CFG_TUD_DFU_RUNTIME, and CFG_TUD_DFU_MODE can be enabled in a single build
+#endif
+
 #endif /* _TUSB_OPTION_H_ */
 
 /** @} */