powerpc/vas: Define VAS_TX_WIN_OPEN ioctl API

Define the VAS_TX_WIN_OPEN ioctl interface for NX GZIP access
from user space. This interface is used to open GZIP send window and
mmap region which can be used by userspace to send requests to NX
directly with copy/paste instructions.
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587114065.2275.1106.camel@hbabu-laptop

Documentation/userspace-api/ioctl/ioctl-number.rst

@@ -286,6 +286,7 @@ Code  Seq#    Include File                                           Comments
 'v'   00-1F  linux/fs.h                                              conflict!
 'v'   00-0F  linux/sonypi.h                                          conflict!
 'v'   00-0F  media/v4l2-subdev.h                                     conflict!
+'v'   20-27  arch/powerpc/include/uapi/asm/vas-api.h		     VAS API
 'v'   C0-FF  linux/meye.h                                            conflict!
 'w'   all                                                            CERN SCI driver
 'y'   00-1F                                                          packet based user level communications

arch/powerpc/include/uapi/asm/vas-api.h

+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Copyright 2019 IBM Corp.
+ */
+
+#ifndef _UAPI_MISC_VAS_H
+#define _UAPI_MISC_VAS_H
+
+#include <asm/ioctl.h>
+
+#define VAS_MAGIC	'v'
+#define VAS_TX_WIN_OPEN	_IOW(VAS_MAGIC, 0x20, struct vas_tx_win_open_attr)
+
+struct vas_tx_win_open_attr {
+	__u32	version;
+	__s16	vas_id;	/* specific instance of vas or -1 for default */
+	__u16	reserved1;
+	__u64	flags;	/* Future use */
+	__u64	reserved2[6];
+};
+
+#endif /* _UAPI_MISC_VAS_H */