ASoC: Add AU1761 audio codec as selectable option

This commit adds the ADI AU1761 audio codec as a selectable option
in the kernel config.  Currently the driver can only be selected
for ADI blackfin devices or if SND_SOC_ALL_CODECS is enabled.

Signed-off-by: Bryce Ferguson <bryce.ferguson@rockwellcollins.com>
Signed-off-by: Mark Brown <broonie@kernel.org>