perf beauty: Move uapi/linux/mount.h copy out of the directory used to build perf

perf beauty: Move uapi/linux/mount.h copy out of the directory used to build perf

It is mostly used only to generate string tables, not to build perf, so
move it to the tools/perf/trace/beauty/include/ hierarchy, that is used
just for scraping.

This is a something that should've have happened, as happened with the
linux/socket.h scrapper, do it now as Ian suggested while doing an
audit/refactor session in the headers used by perf.

No other tools/ living code uses it, just <linux/mount.h> coming from
either 'make install_headers' or from the system /usr/include/
directory.

Suggested-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/CAP-5=fWZVrpRufO4w-S4EcSi9STXcTAN2ERLwTSN7yrSSA-otQ@mail.gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>