fscrypt: log when starting to use inline encryption

When inline encryption is used, the usual message "fscrypt: AES-256-XTS
using implementation <impl>" doesn't appear in the kernel log.  Add a
similar message for the blk-crypto case that indicates that inline
encryption was used, and whether blk-crypto-fallback was used or not.
This can be useful for debugging performance problems.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20220414053415.158986-1-ebiggers@kernel.org