fscrypt: add IV_INO_LBLK_32 support for FS_ENCRYPTION_MODE_PRIVATE

With FS_ENCRYPTION_MODE_PRIVATE (AES-256-XTS inline encryption), add
support for the IV_INO_LBLK_32 IV generation method which adds the
SipHash of the inode number to the file logical block number mod 2^32.
The SipHash key is computed as SHA-256(master_key).

Change-Id: I655e1ac45559d1f327da034b1b64ce55b9ac1597
Signed-off-by: Eric Biggers <ebiggers@google.com>
[neersoni@codeaurora.org: Use first 32 bytes of wrapped master key in sip hash
                          and fix compilation errors]
Signed-off-by: Neeraj Soni <neersoni@codeaurora.org>