camera: Support for HTC's HDR mode

 * HDR was never actually working on CM because we did not instruct the
   camera to take all exposures. The HAL tells us that we'll get one
   JPEG, but we should snap 3 times. We handle this behavior in the
   framework now, but we should honor the num-jpegs-per-shutter value in
   the JPEG callback.

Change-Id: I7124bf08985ae23b21ac4e294fb889ac4106946b