tools: mkimage: set OPENSSL_API_COMPAT

Building with OpenSSL 3.0 produces warnings like:

../tools/sunxi_toc0.c:846:17: warning: ‘RSA_get0_d’ is deprecated:
Since OpenSSL 3.0 [-Wdeprecated-declarations]
  846 |                 if (root_key && RSA_get0_d(root_key)) {
      |                 ^~

As OpenSSL 3.0 is not available in elder Linux distributions
just silence the warning.

Add missing #include <openssl/bn.h>.

Fixes: e9e87ec47c ("tools: mkimage: Add Allwinner TOC0 support")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Tested-by: Andre Przywara <andre.przywara@arm.com>

tools/sunxi_toc0.c

@@ -4,6 +4,8 @@
  * (C) Copyright 2020-2021 Samuel Holland <samuel@sholland.org>
  */
 
+#define OPENSSL_API_COMPAT 0x10101000L
+
 #include <assert.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -11,6 +13,7 @@
 #include <string.h>
 
 #include <openssl/asn1t.h>
+#include <openssl/bn.h>
 #include <openssl/pem.h>
 #include <openssl/rsa.h>