ASoC: Samsung: Do not register samsung audio dma device as pdev

Previously, the ASoC 'platform' (PCM/DMA) object was instantiated via a
platform_device. This didn't represent the hardware well, since there
was no separate hardware associated with this platform_device; it was a
virtual device with sole purpose to call snd_soc_register_platform().

This change removes the platform_device completely. Each Samsung DAI now
registers the ASoC 'platform' itself. Machine drivers are adjusted for
the new 'platform' name.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>