Fix builds on Armv8 systems without AArch64

This fixes "undefined reference to `aes_gcm_dec_128_kernel' in function
`armv8_aes_gcm_decrypt'" and similar

Fixes #16949
Reviewed-by: NPaul Dale <pauli@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16951)

include/crypto/aes_platform.h

@@ -100,7 +100,7 @@ void AES_xts_decrypt(const unsigned char *inp, unsigned char *out, size_t len,
 #    define AES_PMULL_CAPABLE ((OPENSSL_armcap_P & ARMV8_PMULL) && (OPENSSL_armcap_P & ARMV8_AES))
 #    define AES_GCM_ENC_BYTES 512
 #    define AES_GCM_DEC_BYTES 512
-#    if __ARM_MAX_ARCH__>=8
+#    if __ARM_MAX_ARCH__>=8 && defined(__aarch64__)
 #     define AES_gcm_encrypt armv8_aes_gcm_encrypt
 #     define AES_gcm_decrypt armv8_aes_gcm_decrypt
 #     define AES_GCM_ASM(gctx) ((gctx)->ctr==aes_v8_ctr32_encrypt_blocks && \