Have vr flinger take the display after boot on standalones

1. Have vr flinger request the display immediately after boot finishes
on standalones, to prevent incorrectly showing normal 2d content from
surface flinger on the display during startup.

2. If we don't get any surfaces to show for a while after boot finishes,
turn the display off. This should only occur if VrCore is misbehaving
somehow.

Bug: 65742855

Test: - Verified no flickering in the boot anim.

- Verified that if no surfaces are created the display is turned off.

Change-Id: Ibfcd97101334e552d1d562fe4ae9c36877b44397