tools include uapi: Grab a copy of linux/mount.h

tools include uapi: Grab a copy of linux/mount.h

We were using a copy of uapi/linux/fs.h to create the mount syscall
'flags' string table to use in 'perf trace', to convert from the number
obtained via the raw_syscalls:sys_enter into a string, using
tools/perf/trace/beauty/mount_flags.sh, but in de22dd462d04 ("vfs:
Suppress MS_* flag defs within the kernel unless explicitly enabled")
those defines got moved to linux/mount.h, so grab a copy of mount.h too.

Keep the uapi/linux/fs.h as we'll use it for the SEEK_ constants.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-i2ricmpwpdrpukfq3298jr1z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>