blk-crypto: Add support for SM4-XTS blk crypto mode

SM4 is a symmetric cipher algorithm widely used in China. The SM4-XTS
variant is used to encrypt length-preserving data. This is the
mandatory algorithm in some special scenarios.

Add support for the algorithm to block inline encryption. This is needed
for the inlinecrypt mount option to be supported via
blk-crypto-fallback, as it is for the other fscrypt modes.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221201125819.36932-2-tianjia.zhang@linux.alibaba.com