Add support for disabling VDM

Since Virtual Device Manager Service is not gaurenteed to be running on
any given devices, platform code should be prepared for cases where VDM
obtained by getSystemService is null.

This change reinforce platform code where such case could throw
NullPointerException.

Bug: 340929246
Test: Local build with VDM disabled + cts + presubmit
Flag: NONE non-feature update
Change-Id: Id33f7e93bcf7813267434ea6703752af537c09ca