Revert "Remove qrngd"

 * Bring this back. It improves boot time on several devices. The
   built-in seeder is oneshot.

This reverts commit 6969227f7583d279a21ad3fae5c38c065f8706fa.

Change-Id: Ic9e272b7a5d797d06e9a3109328ef6aa0a13b172