[build] Display commands for dependency generation when building with V=1

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile.housekeeping

 define deps_template
 	@$(ECHO) "  [DEPS] $(1)"
 	@$(MKDIR) -p $(BIN)/deps/$(dir $(1))
-	@$(CPP) $(CFLAGS) $(CFLAGS_$(2)) $(CFLAGS_$(3)) -DOBJECT=$(3) \
+	$(Q)$(CPP) $(CFLAGS) $(CFLAGS_$(2)) $(CFLAGS_$(3)) -DOBJECT=$(3) \
 		-Wno-error -M $(1) -MG -MP | \
 		sed 's/\.o\s*:/_DEPS +=/' > $(BIN)/deps/$(1).d
 endef