libcamera: pub_key: Support openssl as an alternative to gnutls

Support verify IPA signatures with openssl as an alternative to gnutls,
to offer more flexibility in the selection of dependencies. Use gnutls
by default, for no specific reason as both are equally well supported.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/pub_key.h

@@ -11,7 +11,9 @@
 
 #include <libcamera/base/span.h>
 
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+struct evp_pkey_st;
+#elif HAVE_GNUTLS
 struct gnutls_pubkey_st;
 #endif
 
@@ -28,7 +30,9 @@ public:
 
 private:
 	bool valid_;
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+	struct evp_pkey_st *pubkey_;
+#elif HAVE_GNUTLS
 	struct gnutls_pubkey_st *pubkey_;
 #endif
 };