perf tools: Update android build documentation

perf tools: Update android build documentation

Update the android build documentation according to recent android build
fixes. The instructions for step 1a and step 2 were updated to work with
NDK version 11(oldest supported version) and NDK version 12(current
version).

Signed-off-by: Chris Phlipot <cphlipot0@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1467349955-1135-5-git-send-email-cphlipot0@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>