Revert "Remove qrngd"

 * Bring this back. It improves boot time on several devices. The
   built-in seeder is oneshot.

This reverts commit 89b023b691148d299bed54b5c4807cfb72e61a4f.

Change-Id: Ic9e272b7a5d797d06e9a3109328ef6aa0a13b172