ASoC: dfbmcs320: make the driver common for other BT modules

DFBM-CS320 is only one of bluetooth modules using CSR bluetooth chips,
we don't want everyone to have a seperate codec driver. anyway, the
feature of Bluetooth SCO is same on all platforms, so this patch
makes the DFBM-CS320 driver become a common BT SCO link driver.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>