d2: fix continuous auto focus

Otherwise continuous autofocus never comes back after a TTF event or
restart preview (turn screen off and then back on)

Change-Id: I252af8dd87c0e28357729daf3f269d7f95eb5c95
d2-common: dex-opt to cache

Cache partition is ~850 MB. We have the space.

Change-Id: I70e0bda7553b6c2dab4aed97feda8b817a9ef3b9