add crosvm to com.android.virt

To do so, crosvm and its dependencies have the apex_available property
set to "//apex_available:platform", "com.android.virt" to explicitly
acknowledge the joining.

Bug: 174639241
Test: m com.android.virt
Change-Id: I2cbb0756d917995e9ee2290194d7b7ee7d4a012b
2 files changed