This adds the serial slave device for the WL1835 Bluetooth interface.

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
CC: Ricardo Salveti <ricardo.salveti@linaro.org>
CC: Tony Lindgren <tony@atomide.com>
CC: Jason Kridner <jkridner@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>