mmc-utils: make use of dependency information generated by gcc

While these dependency information was generated from the start of mmc-utils
it was never used.

Using these informations results in mmc being rebuild when e.g. mmc.h
was touched.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Chris Ball <chris@printf.net>

Makefile

@@ -52,4 +52,6 @@ install: $(progs) install-man
 	$(INSTALL) -m755 -d $(DESTDIR)$(bindir)
 	$(INSTALL) $(progs) $(DESTDIR)$(bindir)
 
+-include $(foreach obj,$(objects), $(dir $(obj))/.$(notdir $(obj)).d)
+
 .PHONY: all clean install manpages install-man