Audio: Allow registering DAP without context

Tests and command line interfaces do not have context, which
artificially prevented them to use the Dynamic Audio Policy API.

Test: adb shell audiorecorder --target /data/file.raw
Bug: 111453086
Change-Id: I3f811f317f7de3282baca308bb5afa5334bf860b
Signed-off-by: Kevin Rocard <krocard@google.com>
Signed-off-by: Robert Berry <robertberry@google.com>