Fix Mouse Shared EP functionality (#14136)

Specifically, if you enable the shared endpoint for mouse reports (or keyboard, which force enables it for mouse), and you don't have mousekeys enabled, it does not properly enable shared mouse EP for pointing device (which uses mouse reports).   This cause it to error out in compiling.  This fixes up some of the logic to ensure that all use cases are supported, and consolidates some of the code.

tmk_core/common.mk

@@ -25,7 +25,8 @@ ifeq ($(strip $(KEYBOARD_SHARED_EP)), yes)
     MOUSE_SHARED_EP = yes
 endif
 
-ifeq ($(strip $(MOUSEKEY_ENABLE)), yes)
+ifeq ($(strip $(MOUSE_ENABLE)), yes)
+    OPT_DEFS += -DMOUSE_ENABLE
     ifeq ($(strip $(MOUSE_SHARED_EP)), yes)
         TMK_COMMON_DEFS += -DMOUSE_SHARED_EP
         SHARED_EP_ENABLE = yes