ASoC: Ux500: Initialise PCM from MSP probe rather than as a device

The PCM is a pseudo-device. It doesn't have any of it's own registers
or hardware. It rather acts as a layer of abstraction for DMA
transfers. Hence, instead of classifying it as a device in its own
right, we call the initialisation from the MSP driver.

Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Ola LILJA2 <ola.o.lilja@stericsson.com>
Cc: alsa-devel@alsa-project.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>