Camera: SoftwareHDR: Reduce mem usage and let exposure time get tuned

- The memory usage has been reduced. Instead of doing 3 bitmaps and
  keeping them in memory, only one bitmap is used and recycled once
  copied to the renderscript allocation.
  In counterpart, I had to remove the software (non-RS) processing.
  I haven't seen any issue of devices disliking RenderScript, so
  I think it's fine.

- I added a config overlay to set the exposure settle time between
  the shots. Some devices are faster than others (ZSL devices can
  take less than 1 second, the previous value). I set this to 0.8
  seconds by default, which works fine on i9100/n7000.

Change-Id: Ia067b717a3754ffb423b29a915d2ae411d04f0b9
camera: Restart the preview if record size changes

  * Needed to release the buffers on many cameras when the record size
    changes but the preview size does not. Without releasing the buffers,
    we can run out of ION space and end up with a mangled recording.

Change-Id: I3ebee850b3e20b3920368c8e052a428f6dd9e3e5