init: Support for initializing virtio-console devices

This change allows init to ensure that a specified virtio-console
device file (`/dev/hvc*`) is available before `ueventd` coldboot.
Times out if device path is not encountered within 10 seconds.

Bug: 325538592
Test: build bertha_x86_64 and bertha_arm64
Change-Id: Ia1512e69ea607bf4d235595caa53668e2dac500c