perf tools: Cleanup doc related targets

Documentation targets handling rules are duplicate.  Consolidate them
with DOC_TARGETS and INSTALL_DOC_TARGETS.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Borislav Petkov <bp@amd64.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1351241752-2919-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>