Change '[ -d ... ] && cmd' to 'if [ -d ... ]; then cmd; fi' to avoid make errors if the condition is false
If $(PLATFORM_DIR)/files exists, copy it into the kernel tree on prepare.
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@6263 3c298f89-4303-0410-b956-a3cf2f4a3e73