BACKPORT: FROMLIST: fscrypt: add inline encryption support

Add support for inline encryption to fs/crypto/.  With "inline
encryption", the block layer handles the decryption/encryption as part
of the bio, instead of the filesystem doing the crypto itself via
Linux's crypto API.  This model is needed in order to take advantage of
the inline encryption hardware present on most modern mobile SoCs.

To use inline encryption, the filesystem needs to be mounted with
'-o inlinecrypt'.  The contents of any AES-256-XTS encrypted files will
then be encrypted using blk-crypto, instead of using the traditional
filesystem-layer crypto.  fscrypt still provides the key and IV to use,
and the actual ciphertext on-disk is still the same; therefore it's
testable using the existing fscrypt ciphertext verification tests.

Note that since blk-crypto has a fallack to Linux's crypto API, this
feature is usable and testable even without actual inline encryption
hardware.

Per-filesystem changes will be needed to set encryption contexts when
submitting bios and to implement the 'inlinecrypt' mount option.  This
patch just adds the common code.

Bug: 137270441
Test: tested as series; see I26aac0ac7845a9064f28bb1421eb2522828a6dec
Change-Id: I238b5484f3798dd4d829be5535234b53951db0ea
Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Link: https://patchwork.kernel.org/patch/11214761/