Move architecture specific config.mk files into subdirs

This cleans up U-Boot's toplevel directory a bit and makes the
architecture 'config.mk' file naming and location similar to board
and cpu 'config.mk' files
Signed-off-by: NPeter Tyser <ptyser@xes-inc.com>

config.mk

@@ -83,7 +83,7 @@ RANLIB	= $(CROSS_COMPILE)RANLIB
 sinclude $(OBJTREE)/include/autoconf.mk
 
 ifdef	ARCH
-sinclude $(TOPDIR)/$(ARCH)_config.mk	# include architecture dependend rules
+sinclude $(TOPDIR)/lib_$(ARCH)/config.mk	# include architecture dependend rules
 endif
 ifdef	CPU
 sinclude $(TOPDIR)/cpu/$(CPU)/config.mk	# include  CPU	specific rules