Use vpaes + conversion to setup CBC decrypt on NEON.

Our bsaes CBC decrypt implementation does not need a block128_f, so we
can just convert the key once and move on.

Bug: 256
Change-Id: Ie96571a479c74734a12318c2210066eb7be0971c
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/37428
Reviewed-by: Adam Langley <agl@google.com>

crypto/fipsmodule/cipher/e_aes.c

diff --git a/crypto/fipsmodule/cipher/e_aes.c b/crypto/fipsmodule/cipher/e_aes.c
index bc90649..685d2db 100644
--- a/crypto/fipsmodule/cipher/e_aes.c
+++ b/crypto/fipsmodule/cipher/e_aes.c
@@ -110,7 +110,10 @@
         dat->stream.cbc = aes_hw_cbc_encrypt;
       }
     } else if (bsaes_capable() && mode == EVP_CIPH_CBC_MODE) {
-      ret = aes_nohw_set_decrypt_key(key, ctx->key_len * 8, &dat->ks.ks);
+      ret = vpaes_set_decrypt_key(key, ctx->key_len * 8, &dat->ks.ks);
+      if (ret == 0) {
+        vpaes_decrypt_key_to_bsaes(&dat->ks.ks, &dat->ks.ks);
+      }
       // If |dat->stream.cbc| is provided, |dat->block| is never used.
       dat->block = NULL;
       dat->stream.cbc = bsaes_cbc_encrypt;