Remove VSoCEnabled() and replace it with config's enable_ivserver()

The VSoCEnabled function was meant to be only transitional.
The ivserver is basically the provider of the vsoc hardware so it
doesn't make a lot of sense to add a different flag for it.
The config object has a function enable_ivserver() which simply checks
the value of the hardware_name config property.

Bug: 122978436
Test: build & run locally

Change-Id: I9f6a1e472c8928002fa0691a47f471bc2acc591b