Set virtual_camera_service_enabled soong config variable

... based on RELEASE_PACKAGE_VIRTUAL_CAMERA build flag.

Bug: 301023410
Bug: 318088136
Test: build with RELEASE_PACKAGE_VIRTUAL_CAMERA enabled / disabled
Ignore-AOSP-First: virtual camera is not (yet) merged in AOSP

Change-Id: Icd295052381831b30c2835f64dec7b08352d4708