ASoC: add sport driver for bf6xx soc

The SPORT(Serial Port) module on bf6xx soc has a totally different ip
comparing to bf5xx soc. An individual SPORT module consists of two
independently configurable SPORT halves with identical functionality.
Each SPORT half can be configured for either transmitter or receiver.

Signed-off-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>