xen: update missing ioctl magic numers documentation

Add missing ioctl "magic numbers" for various Xen interfaces
(xenbus_dev.h, gntalloc.h, gntdev.h, and privcmd.h).
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org
Link: https://lore.kernel.org/r/20220131161959.16509-1-rdunlap@infradead.orgSigned-off-by: Juergen Gross <jgross@suse.com>

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

@@ -115,6 +115,7 @@ Code  Seq#    Include File                                           Comments
 'B'   00-1F  linux/cciss_ioctl.h                                     conflict!
 'B'   00-0F  include/linux/pmu.h                                     conflict!
 'B'   C0-FF  advanced bbus                                           <mailto:maassen@uni-freiburg.de>
+'B'   00-0F  xen/xenbus_dev.h                                        conflict!
 'C'   all    linux/soundcard.h                                       conflict!
 'C'   01-2F  linux/capi.h                                            conflict!
 'C'   F0-FF  drivers/net/wan/cosa.h                                  conflict!
@@ -134,6 +135,7 @@ Code  Seq#    Include File                                           Comments
 'F'   80-8F  linux/arcfb.h                                           conflict!
 'F'   DD     video/sstfb.h                                           conflict!
 'G'   00-3F  drivers/misc/sgi-gru/grulib.h                           conflict!
+'G'   00-0F  xen/gntalloc.h, xen/gntdev.h                            conflict!
 'H'   00-7F  linux/hiddev.h                                          conflict!
 'H'   00-0F  linux/hidraw.h                                          conflict!
 'H'   01     linux/mei.h                                             conflict!
@@ -176,6 +178,7 @@ Code  Seq#    Include File                                           Comments
 'P'   60-6F  sound/sscape_ioctl.h                                    conflict!
 'P'   00-0F  drivers/usb/class/usblp.c                               conflict!
 'P'   01-09  drivers/misc/pci_endpoint_test.c                        conflict!
+'P'   00-0F  xen/privcmd.h                                           conflict!
 'Q'   all    linux/soundcard.h
 'R'   00-1F  linux/random.h                                          conflict!
 'R'   01     linux/rfkill.h                                          conflict!