cyrpto/b128ops: Remove struct u128

Per git-grep u128_xor() and its related struct u128 are unused except
to implement {be,le}128_xor(). Remove them to free up the namespace.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230531132323.314826687@infradead.org

[CRYPTO] lib: some common 128-bit block operations, nicely centralized

128bit is a common blocksize in linux kernel cryptography, so it helps to
centralize some common operations.

The code, while mostly trivial, is based on a header file mode_hdr.h in
http://fp.gladman.plus.com/AES/modes.vc8.19-06-06.zip

The original copyright (and GPL statement) of the original author,
Dr Brian Gladman, is preserved.

Signed-off-by: Rik Snel <rsnel@cube.dyndns.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>