Audio V4: Move audio HIDL wrapper in a 2.0 folder

This will allow for an easy review of the next patch that splits the
implementation to support multiple version.

Bug: 38184704
Test: compile
Change-Id: I3e8fc3b41aaf2dd8061bd2a3566810efa67c7f9f
Signed-off-by: Kevin Rocard <krocard@google.com>