crypto: sha256: Add mechanism to keep C code as fallback for SHA256_ASM

crypto: sha256: Add mechanism to keep C code as fallback for SHA256_ASM

Currently, architectures have to decide if they want the C code or an
arch-specific implementation. Let's add a macro, that allows to keep the C
code even if SHA256_ASM is defined (but rename it from sha256_block_data_order
to sha256_block_data_order_c). The macro INCLUDE_C_SHA256 can be used by
architectures, that want the C code as fallback code.

Signed-off-by: Charalampos Mitrodimas <charalampos.mitrodimas@vrull.eu>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21923)