Create VirtualCameraController iff all required flags are enabled.

This cl also adds check for the build flag indicating that the
virtual_camera service is present in the build - otherwise attempt
to fetch the service will cause service manager to wait indefinitely
for service start.

Bug: 301023410
Test: atest VirtualCameraTest with build flag enabled / disabled
Change-Id: I48c79579a6ca049578eb9f1ca662d5801972c259