audioflinger: Allow mixed use of JB A2DP HALs and ICS policy

Old policies don't address the modules by handle and expect them
all to be scanned for supported devices; new modules stopped
listing supported devices. The combination of a new A2DP with
an old policy left policy unable to find A2DP outputs, so the
new HALs couldn't be used.

So... if an old policy is in use, searching for an A2DP output,
and finds a non-primary HAL that doesn't list any device, assume
it's A2DP and use it.

Change-Id: Ie946c065b5c325afd02ba3437077f634e079b386