lib/crypto: arm/ghash: Migrate optimized code into library

lib/crypto: arm/ghash: Migrate optimized code into library

Remove the "ghash-neon" crypto_shash algorithm.  Move the corresponding
assembly code into lib/crypto/, and wire it up to the GHASH library.

This makes the GHASH library be optimized on arm (though only with NEON,
not PMULL; for now the goal is just parity with crypto_shash).  It
greatly reduces the amount of arm-specific glue code that is needed, and
it fixes the issue where this optimization was disabled by default.

To integrate the assembly code correctly with the library, make the
following tweaks:

- Change the type of 'blocks' from int to size_t.
- Change the types of 'dg' and 'h' to polyval_elem.  Note that this
  simply reflects the format that the code was already using, at least
  on little endian CPUs.  For big endian CPUs, add byte-swaps.
- Remove the 'head' argument, which is no longer needed.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20260319061723.1140720-8-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>