ASoC: allow drivers to compile both static and dynamic

Based on where the code is synced the driver should allow
both static and dynamic linked compilation.
Also remove __exit for modules loaded from another common
init/exit functions.

Change-Id: Ib58f152002aba3af4446f9bbd9b82c279212bd0a
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>