audio AIDL: Consider `BUS` devices as attached

After analyzing Auto APM config files and checking with
the Auto team, it has turned out that `BUS` devices are
considered to be permanently attached. In the AIDL schema
that means, they must have an empty connection type.

A solution which seems to work well is to map AIDL types
`IN_|OUT_DEVICE` with no connection to legacy BUS devices.

Bug: 303926380
Test: atest audio_aidl_ndk_conversion_tests
(cherry picked from commit ef65be72)
Change-Id: Ie1b03a5c302d2fa0c176cd420f4156aaa2ed0257