lib/crypto: powerpc/aes: Migrate POWER8 optimized code into library

lib/crypto: powerpc/aes: Migrate POWER8 optimized code into library

Move the POWER8 AES assembly code into lib/crypto/, wire the key
expansion and single-block en/decryption functions up to the AES library
API, and remove the superseded "p8_aes" crypto_cipher algorithm.

The result is that both the AES library and crypto_cipher APIs are now
optimized for POWER8, whereas previously only crypto_cipher was (and
optimizations weren't enabled by default, which this commit fixes too).

Note that many of the functions in the POWER8 assembly code are still
used by the AES mode implementations in arch/powerpc/crypto/.  For now,
just export these functions.  These exports will go away once the AES
modes are migrated to the library as well.  (Trying to split up the
assembly file seemed like much more trouble than it would be worth.)

Another challenge with this code is that the POWER8 assembly code uses a
custom format for the expanded AES key.  Since that code is imported
from OpenSSL and is also targeted to POWER8 (rather than POWER9 which
has better data movement and byteswap instructions), that is not easily
changed.  For now I've just kept the custom format.  To maintain full
correctness, this requires executing some slow fallback code in the case
where the usability of VSX changes between key expansion and use.  This
should be tolerable, as this case shouldn't happen in practice.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20260112192035.10427-14-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>