buildroot; move defconfigs to configs/ and print in help

As discussed earlier on the mailing list. It simplifies code, gives more
sensible error message on typos and makes the defconfigs easier to find
for users.

Furthermore, update documentation to match.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -591,9 +591,9 @@ endif # ifeq ($(BR2_HAVE_DOT_CONFIG),y)
 flush:
 	rm -f $(BUILD_DIR)/tgt-config.cache
 
-%_defconfig: $(CONFIG)/conf
-	cp $(shell find ./target/ -name $@) .config
-	-@$(MAKE) oldconfig
+%_defconfig: $(TOPDIR)/configs/%_defconfig
+	cp $^ .config
+	@$(MAKE) oldconfig
 
 configured: dirs host-sed kernel-headers uclibc-config busybox-config linux26-config
 
@@ -628,6 +628,9 @@ help:
 	@echo '  external-deps          - list external packages used'
 	@echo '  flush                  - flush configuration cache'
 	@echo
+	@$(foreach b, $(notdir $(wildcard $(TOPDIR)/configs/*_defconfig)), \
+	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
+	@echo
 	@echo 'See docs/README and docs/buildroot.html for further details'
 	@echo
 

docs/buildroot.html

@@ -646,22 +646,15 @@ endif
 
       <li>Then, in the
       <code>target/device/yourcompany/project-foobar/</code>
-      directory, you can store different files:
+      directory, you can store configuration files for the kernel,
+      for Busybox or uClibc.
 
-      <ul>
-
-	<li>One or more Buildroot configurations, under file named
-	<code>something_defconfig</code>. Your users will then be able
-	to run <code>make something_defconfig</code> and get the right
-	configuration for your project</li>
-
-	<li>Configuration files for the kernel, for Busybox or
-	uClibc. These files can then be referenced by the Buildroot
-	configuration described above</li>
-
-      </ul>
-
-      </li>
+      You can furthermore create one or more preconfigured configuration
+      files, referencing those files. These config files are named
+      <code>something_defconfig</config> and are stored in the toplevel
+      <code>configs/</code> directory. Your users will then be able
+      to run <code>make something_defconfig</code> and get the right
+      configuration for your project</li>
 
     </ol>