Make:Use "simply expanded" make variables.

Replace some "recursively expanded" make variables with "simply
expanded" variables (i.e. replace = with :=). This has no functional
impact but is more consistent and theoretically more efficient.

Change-Id: Iaf33d7c8ad48464ae0d39923515d1e7f230c95c1
diff --git a/Makefile b/Makefile
index 1eb0174..c20bf91 100644
--- a/Makefile
+++ b/Makefile
@@ -125,10 +125,10 @@
 
 # Verbose flag
 ifeq (${V},0)
-        Q=@
+        Q:=@
         CHECKCODE_ARGS	+=	--no-summary --terse
 else
-        Q=
+        Q:=
 endif
 export Q