perf tools: Try to build Documentation when installing

There's a portion in the "perf list" output refering to the exact
specification of raw hardware events.

Since this description is in the perf-list manpage, try to build and
install the man pages, warning the user when that is not possible
due to missing packages (xmlto and asciidoc).

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-ij71ysszkdvz3fy3wr331bke@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>