Adding 'plugins' target along with the libtraceevent.a, so plugins are
built together with traceevent library.

Adding 'install-traceevent-plugins' Makefile install target, instructing
perf to install plugins into:

  $(HOME)/.traceevent/plugins
    - If installed localy under $HOME

  $(DESTDIR)/$(prefix)/$(libdir)/traceevent/plugins
    - If installed globally

Examples:
  $ make install
  ...
  $ find ~/.traceevent/plugins/
  /home/jolsa/.traceevent/plugins/
  /home/jolsa/.traceevent/plugins/plugin_mac80211.so
  /home/jolsa/.traceevent/plugins/plugin_kvm.so
  /home/jolsa/.traceevent/plugins/plugin_scsi.so
  /home/jolsa/.traceevent/plugins/plugin_sched_switch.so
  /home/jolsa/.traceevent/plugins/plugin_xen.so
  /home/jolsa/.traceevent/plugins/plugin_cfg80211.so
  /home/jolsa/.traceevent/plugins/plugin_function.so
  /home/jolsa/.traceevent/plugins/plugin_kmem.so
  /home/jolsa/.traceevent/plugins/plugin_hrtimer.so
  /home/jolsa/.traceevent/plugins/plugin_jbd2.so

  $ sudo make install DESTDIR=/opt/perf/
  ...
  $ find /opt/perf/lib64/traceevent/plugins/
  /opt/perf/lib64/traceevent/plugins/
  /opt/perf/lib64/traceevent/plugins/plugin_kvm.so
  /opt/perf/lib64/traceevent/plugins/plugin_scsi.so
  /opt/perf/lib64/traceevent/plugins/plugin_mac80211.so
  /opt/perf/lib64/traceevent/plugins/plugin_hrtimer.so
  /opt/perf/lib64/traceevent/plugins/plugin_kmem.so
  /opt/perf/lib64/traceevent/plugins/plugin_jbd2.so
  /opt/perf/lib64/traceevent/plugins/plugin_sched_switch.so
  /opt/perf/lib64/traceevent/plugins/plugin_function.so
  /opt/perf/lib64/traceevent/plugins/plugin_cfg80211.so
  /opt/perf/lib64/traceevent/plugins/plugin_xen.so
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1386076182-14484-8-git-send-email-jolsa@redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>