Reorganize kernel configs - target/linux/*/config is now a directory.

Reorganize kernel configs - target/linux/*/config is now a directory.
./config/default will replace the old config and config-diff (format is like
config-diff, the full kernel config is no longer kept in the build system)
This commit removes all the kernel config stuff, the next one will add
the replacement - there's no way to do this atomically with svn.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@6337 3c298f89-4303-0410-b956-a3cf2f4a3e73