Enable MJPEG HW decode accelerator on Intel CrOS platforms

Enable MJPEG HW decode accelerator on Intel CrOS platforms

Following are the performance numbers for apprtc.appspot.com test
(no loopback) on Peppy.

With cpu governer = performance,
               SW     HW
latency(ms)    7.3    5.2
total CPU(%)  21.6   12.9
power (mWh/s)  2.2    2.2

With default cpu governer = ondemand,
               SW     HW
latency(ms)   10.3    5.5
total CPU(%)  27.4   22.1
power (mWh/s)  2.22   2.21

BUG=426381
TEST=test apprtc on squawks.

Review URL: https://codereview.chromium.org/1260923002

Cr-Commit-Position: refs/heads/master@{#341072}