Add a function to lookup ssp devices from device tree. This way, users
can reference the ssp devices in order to register to them.
Signed-off-by: NDaniel Mack <zonque@gmail.com>
Acked-by: NHaojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: NMark Brown <broonie@linaro.org>