Move the contents of arch/arm/lib/crypto/ into lib/crypto/arm/.

The new code organization makes a lot more sense for how this code
actually works and is developed.  In particular, it makes it possible to
build each algorithm as a single module, with better inlining and dead
code elimination.  For a more detailed explanation, see the patchset
which did this for the CRC library code:
https://lore.kernel.org/r/20250607200454.73587-1-ebiggers@kernel.org/.
Also see the patchset which did this for SHA-512:
https://lore.kernel.org/linux-crypto/20250616014019.415791-1-ebiggers@kernel.org/

This is just a preparatory commit, which does the move to get the files
into their new location but keeps them building the same way as before.
Later commits will make the actual improvements to the way the
arch-optimized code is integrated for each algorithm.

Add a gitignore entry for the removed directory arch/arm/lib/crypto/ so
that people don't accidentally commit leftover generated files.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20250619191908.134235-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Instead of providing crypto_shash algorithms for the arch-optimized
SHA-256 code, instead implement the SHA-256 library.  This is much
simpler, it makes the SHA-256 library functions be arch-optimized, and
it fixes the longstanding issue where the arch-optimized SHA-256 was
disabled by default.  SHA-256 still remains available through
crypto_shash, but individual architectures no longer need to handle it.

To merge the scalar, NEON, and CE code all into one module cleanly, add
!CPU_V7M as a direct dependency of the CE code.  Previously, !CPU_V7M
was only a direct dependency of the scalar and NEON code.  The result is
still the same because CPU_V7M implies !KERNEL_MODE_NEON, so !CPU_V7M
was already an indirect dependency of the CE code.

To match sha256_blocks_arch(), change the type of the nblocks parameter
of the assembly functions from int to size_t.  The assembly functions
actually already treated it as size_t.

While renaming the assembly files, also fix the naming quirk where
"sha2" meant sha256.  (SHA-512 is also part of SHA-2.)

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Continue disentangling the crypto library functions from the generic
crypto infrastructure by moving the arm BLAKE2s, ChaCha, and Poly1305
library functions into a new directory arch/arm/lib/crypto/ that does
not depend on CRYPTO.  This mirrors the distinction between crypto/ and
lib/crypto/.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>