tools: Add a help target

... and make it the default one so that calling 'make' without arguments
in the tools/ directory gives you the possible targets to build along
with a short description of what they are.
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: http://lkml.kernel.org/r/1334162178-17152-5-git-send-email-bp@amd64.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/Makefile

 include scripts/Makefile.include
 
+help:
+	@echo 'Possible targets:'
+	@echo ''
+	@echo '  cpupower   - a tool for all things x86 CPU power'
+	@echo '  firewire   - the userspace part of nosy, an IEEE-1394 traffic sniffer'
+	@echo '  lguest     - a minimal 32-bit x86 hypervisor'
+	@echo '  perf       - Linux performance measurement and analysis tool'
+	@echo '  selftests  - various kernel selftests'
+	@echo '  turbostat  - Intel CPU idle stats and freq reporting tool'
+	@echo '  usb        - USB testing tools'
+	@echo '  virtio     - vhost test module'
+	@echo '  vm         - misc vm tools'
+	@echo '  x86_energy_perf_policy - Intel energy policy tool'
+	@echo ''
+	@echo 'Cleaning targets:'
+	@echo ''
+	@echo '  all of the above with the "_clean" string appended cleans'
+	@echo '    the respective build directory.'
+	@echo '  clean: a summary clean target to clean _all_ folders'
+
 cpupower: FORCE
 	$(QUIET_SUBDIR0)power/$@/ $(QUIET_SUBDIR1)