tools headers UAPI: Sync linux/mman.h with the kernel

To get the changes in:

  e346b381 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")

Add that to 'perf trace's mremap 'flags' decoder.

This silences this perf build warning:

  Warning: Kernel ABI header at 'tools/include/uapi/linux/mman.h' differs from latest version at 'include/uapi/linux/mman.h'
  diff -u tools/include/uapi/linux/mman.h include/uapi/linux/mman.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Brian Geffon <bgeffon@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>