g2: dexopt system to /cache

http://review.cyanogenmod.org/#/c/56059/ set dexopt to /data only
by default.  g2 has nearly 700MB on /cache so let's continue to use it.

Signed-off-by: houst0nn <houstonn@gmail.com>
Updates from houst0nn

g2: Force full GLES virtual layers to go via HWC

g2: adreno source=false

g2: Enable smooth-streaming video-playback

credits: houst0nn