libvpx

Enable more split modes for animated content.

For content that is identified as likely to contain some
animation or graphics content, increase the availability
of split modes for good quality speeds 1-3.

On a problem test animation clip this improves metrics
results by about 0.25 db and makes a noticeable difference
visually. It also causes a small drop in file size (~0.5%) but
a rise in encode time of about 5-6% at speed  2.

For more normal content it should have no effect.

Change-Id: Ic4cd9a8de065af9f9402f4477a17442aebf0e439