ARM: ux500: Stop registering the PCM driver from platform code

We now initialise the PCM driver through the MSP DAI, so there is
no need to register it though platform code anymore. This patch
strips out all PCM platform registration.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>