kconfig: integrate split config into silentoldconfig

Now that kconfig can load multiple configurations, it becomes simple to
integrate the split config step, by simply comparing the new .config file with
the old auto.conf (and then saving the new auto.conf).  A nice side effect is
that this saves a bit of disk space and cache, as no data needs to be read
from or saved into the splitted config files anymore (e.g.  include/config is
now 648KB instead of 5.2MB).

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/xtensa/Makefile b/arch/xtensa/Makefile
index 98fac848..3a3a4c6 100644
--- a/arch/xtensa/Makefile
+++ b/arch/xtensa/Makefile
@@ -71,7 +71,7 @@
 # Update machine cpu and platform symlinks if something which affects
 # them changed.
 
-$(archinc)/.platform: $(wildcard include/config/arch/*.h) include/config/MARKER
+$(archinc)/.platform: $(wildcard include/config/arch/*.h) include/config/auto.conf
 	@echo '  SYMLINK $(archinc)/xtensa/config -> $(archinc)/xtensa/config-$(CPU)'
 	$(Q)mkdir -p $(archinc)
 	$(Q)mkdir -p $(archinc)/xtensa