tools/include: Add pfn.h stub

Add a stubbed pfn header with definitions used in testing.
Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/1bdc02125963f945bf90dd8cb37c404cc0688af2.1643796665.git.karolinadrobnik@gmail.com

tools/include/linux/pfn.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TOOLS_LINUX_PFN_H_
+#define _TOOLS_LINUX_PFN_H_
+
+#include <linux/mm.h>
+
+#define PFN_UP(x)	(((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)
+#define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
+#define PFN_PHYS(x)	((phys_addr_t)(x) << PAGE_SHIFT)
+#endif