ARM: ux500: Remove superfluous 'psize' attribute from Audio platform data

'psize' is used to calculate the maximum DMA burst size. However it
is only taken into consideration when editing the DMA channel's
configuration. The Audio DMA platform data is only used to allocate
a channel, not configure it. That will be done at a later date within
the MSP driver.

We're also removing comments which are no longer required, as
'data_width' is no longer set in any device's platform data period.

Tested-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>