make: rename AD variable to Q

Makefile.include

@@ -83,10 +83,10 @@ endif
 QUIET ?= 1
 
 ifeq ($(QUIET),1)
-  AD=@
+  Q=@
   MAKEFLAGS += --no-print-directory
 else
-  AD=
+  Q=
 endif
 
 # Fail on warnings. Can be overridden by `make WERROR=0`.

Makefile.vars

-export AD                    # Used in front of Makefile lines to suppress the printing of the command if user did not opt-in to see them.
+export Q                     # Used in front of Makefile lines to suppress the printing of the command if user did not opt-in to see them.
 export QUIET                 # The parameter to use whether to show verbose makefile commands or not.
 
 export APPLICATION           # The application, set in the Makefile which is run by the user.