sparc: fix bootloader build

- Add various missing jamfiles
- Add required implementation stubs
- Update openfirmware jamfiles for multiboot support
- Update linker rules for sparc loader

Change-Id: I2d06c7a4d33827f58d82946687003f9a0dcb1b7d
Reviewed-on: https://review.haiku-os.org/c/1329
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/boot/platform/openfirmware/support.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2006-2011, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Alexander von Gluck, [email protected]
+ */
+#ifndef SUPPORT_H
+#define SUPPORT_H
+
+
+#include <OS.h>
+
+
+bigtime_t system_time(void);
+int32 of_address_cells(int package);
+int32 of_size_cells(int package);
+
+#endif