Do not complain when /dev/crypto does not exist.

FreeBSD does not enable cryptodev(4) by default.  OpenBSD disabled support
for /dev/crypto by default from 4.9 and removed it from 5.7.  Now the engine
is properly enabled by default on BSD platforms (see #7885), it continuously
complains:

Could not open /dev/crypto: No such file or directory

Hide the nagging error message behind ENGINE_DEVCRYPTO_DEBUG.

CLA: trivial
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NMatthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7896)

(cherry picked from commit c79a022da973140c141eeebff9170ca5702be0f9)

crypto/engine/eng_devcrypto.c

@@ -24,6 +24,8 @@
 
 #include "internal/engine.h"
 
+/* #define ENGINE_DEVCRYPTO_DEBUG */
+
 #ifdef CRYPTO_ALGORITHM_MIN
 # define CHECK_BSD_STYLE_MACROS
 #endif
@@ -736,7 +738,10 @@ void engine_load_devcrypto_int()
     ENGINE *e = NULL;
 
     if ((cfd = open("/dev/crypto", O_RDWR, 0)) < 0) {
-        fprintf(stderr, "Could not open /dev/crypto: %s\n", strerror(errno));
+#ifndef ENGINE_DEVCRYPTO_DEBUG
+        if (errno != ENOENT)
+#endif
+            fprintf(stderr, "Could not open /dev/crypto: %s\n", strerror(errno));
         return;
     }