Camera: Initialize the camera shutter sounds asynchronously.

As part of the camera initialization, the shutter sounds(for both
snapshot and recording) are loaded. This takes around 70ms. Since
the launch is not dependent on this, the sounds can be loaded
asynchronously. Hence moving them to a seperate thread.

Change-Id: Id0309febf0742cadc3bcca71b0f19064547b6bda