ASoC: davinci-mcasp: Rename platform data struct

Rename the struct for the platform data:
snd_platform_data -> davinci_mcasp_pdata

Since we have users under arch/arm/mach-davinci/ for this struct add
temporary define to avoid breakage. The arch code can be updated later to
use the new struct name.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>