The defconfig fetches Linux and U-Boot from a git repo using the
unauthenticated git:// protocol, so add download hashes for them to ensure
we get the right sources by adding a global patch dir and running
utils/add-custom-hashes.
The defconfig uses the Linux sources for the kernel headers, so make
linux-headers/linux-headers.hash a symlink to linux/linux.hash so the same
hash file is used.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
