Provide an additional pair of #defines, MBEDTLS_SHA512_USE_A64_CRYPTO_IF_PRESENT
and MBEDTLS_SHA512_USE_A64_CRYPTO_ONLY. At most one of them may be
specified. If used, it is necessary to compile with -march=armv8.2-a+sha3.
The MBEDTLS_SHA512_PROCESS_ALT and MBEDTLS_SHA512_ALT mechanisms
continue to work, and are mutually exclusive with SHA512_USE_A64_CRYPTO.
There should be minimal code size impact if no A64_CRYPTO option is set.
The SHA-512 implementation was originally written by Simon Tatham for PuTTY,
under the MIT licence; dual-licensed as Apache 2 with his kind permission.
Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
