add get_achievable_rates.py under cts-media tools

This script can be used to generate media_codecs_performance.xml
required for Android 6.0 (and above) as described in
http://source.android.com/devices/media/oem.html .

Bug: 23587558
Change-Id: I754779b559b0fe38a9794358fa29490a79fca00b
1 file changed