servicemanager: preload vintf manifest

Doing this asynchronously since it was delaying first client by ~6ms on
crosshatch and other devices.

Bug: 144282062
Test: on walleye, StartVibratorService ~9ms -> ~4ms.
Change-Id: I6cc65e74922b32c2e7135f583fa892fa26f85e2b
1 file changed