Increase touch video buffer size

We are currently limited to having 10 buffers max inside a
TouchVideoDevice. That means that if too many frames are generated, we
will start dropping them. The dropped frames will never make it to the
InputClassifier HAL.

Now that touch is at 180 Hz, this becomes even more of a problem. If the
system is running slow, it is easy to overrun the buffer.

Increase the buffer size to avoid dropping frames.

Bug: 160016140
Test: none
Change-Id: I3662236a518e908cec94c31bf7604eb830c3308a