BACKPORT: FROMLIST: fscrypt: invoke crypto API for ESSIV handling

Instead of open-coding the calculations for ESSIV handling, use an ESSIV
skcipher which does all of this under the hood.  ESSIV was added to the
crypto API in v5.4.

This is based on a patch from Ard Biesheuvel, but reworked to apply
after all the fscrypt changes that went into v5.4.

Tested with 'kvm-xfstests -c ext4,f2fs -g encrypt', including the
ciphertext verification tests for v1 and v2 encryption policies.

Change-Id: Id0e3cc38fcd9a25a4d55cf19c1b87e5798bf7d90
Originally-from: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Link: https://patchwork.kernel.org/patch/11182383/