mkimage: fix openssl 1.1.x compat fix with libressl

libressl sets OPENSSL_VERSION_NUMBER to 0x20000000L, which breaks API
checks based on it.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

tools/mkimage/patches/210-openssl-1.1.x-compat.patch

@@ -11,7 +11,7 @@
  #define HAVE_ERR_REMOVE_THREAD_STATE
  #endif
  
-+#if OPENSSL_VERSION_NUMBER < 0x10100005L
++#if (OPENSSL_VERSION_NUMBER < 0x10100005L) || defined(LIBRESSL_VERSION_NUMBER)
 +static void RSA_get0_key(const RSA *r,
 +                         const BIGNUM **n, const BIGNUM **e, const BIGNUM **d)
 +{