Use asm/unaligned.h instead of linux/unaligned/access_ok.h for unaligned
access. This is needed on architectures that doesn't handle unaligned
accesses directly.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

Now btrfs can utilize the newly intorudced BLAKE2 hash.

Signed-off-by: Qu Wenruo <wqu@suse.com>

This mostly crossports crypto/hash.[ch] from btrfs-progs.

The differences are:
- No blake2 support
  No blake2 related library in U-Boot yet.

- Use uboot xxhash/sha256 directly
  No need to implement the code as U-Boot has already provided the
  interface.

This adds the support for the following csums:
- SHA256
- XXHASH

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Marek Behún <marek.behun@nic.cz>