Watch for SurfaceFlinger death

The ComposerService object wasn't watching for SurfaceFlinger
restarts, which doesn't usually matter because the app framework
restarts when SurfaceFlinger dies.  However, mediaserver continues
to run, which means its ComposerService object was trying to use
a dead handle, and playback of DRM movies was failing.

This adds a DeathRecipient listener and some logic to re-establish
the SurfaceFlinger connection.

Bug 6645813

Change-Id: I07581b881d3835601aa57d5358c8259d93bc4515