Annotate the structs that will be moved to hmac_local.h and evp_locl.h

Annotate the structs that will be moved to hmac_local.h and evp_locl.h
in an upcoming bump.  This omits EVP_AEAD_CTX which will be dealt with
separately. EVP_CIPHER_INFO internals are still publicly visible in
OpenSSL, so it won't be moved.

Move typedefs for HMAC_CTX and EVP_ENCODE_CTX to ossl_typ.h.  These
typedefs will be visible by files including only hmac.h or evp.h since
hmac.h includes evp.h and evp.h includes ossl_typ.h.

ok inoguchi