kbuild: teach mkmakfile to be silent

With this fix a "make -s" is now really silent

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/mkmakefile b/scripts/mkmakefile
index e65d8b3..67d59c7 100644
--- a/scripts/mkmakefile
+++ b/scripts/mkmakefile
@@ -17,7 +17,9 @@
 then
 	exit 0
 fi
-echo "  GEN     $2/Makefile"
+if [ "${quiet}" != "silent_" ]; then
+	echo "  GEN     $2/Makefile"
+fi
 
 cat << EOF > $2/Makefile
 # Automatically generated by $0: don't edit