crypto: x86/aes-gcm - reorder AVX512 precompute and aad_update functions

crypto: x86/aes-gcm - reorder AVX512 precompute and aad_update functions

Now that the _aes_gcm_precompute macro is instantiated only once,
replace it directly with a function definition.

Also, move aes_gcm_aad_update_vaes_avx512() to a different location in
the file so that it's consistent with aes-gcm-vaes-avx2.S and also the
BoringSSL port of this code.

No functional changes.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20251002023117.37504-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>