Makefile: cosmetic improvement for ARCH/BRANCH output

This should save a few repetitive lines during multi image build,
albeit the ideal result should only print out the BRANCH once
as it's invariant for the whole build process (no, you can't
just go ahead and echo it where it gets checked/defined
since that's not the recipe body).
Suggested by mike@

Makefile

@@ -69,13 +69,12 @@ SHELL = /bin/bash
 	else \
 		say "** goal: $@"; \
 	fi; \
-	say "** BRANCH: $(BRANCH)"; \
 	for ARCH in $(ARCHES); do \
 		if [ -z "$(QUIET)" ]; then \
 			if [ "$$ARCH" != "$(firstword $(ARCHES))" ]; then \
 				say; \
 			fi; \
-			say "** ARCH: $$ARCH"; \
+			say "** BRANCH/ARCH: $(BRANCH)/$$ARCH"; \
 		fi; \
 		if [ -n "$(REPORT)" ] && [ -n "$(DEBUG)" ] && [ -z "$(CHECK)" ]; then \
 			REPORT_PATH=$$(mktemp --tmpdir mkimage-profiles.report.XXXXXXX); \