g:18:     symbol SND_AT91_SOC_SAM9G20_WM8731 depends on ATMEL_SSC

SND_ATMEL_SOC_SSC needs ATMEL_SSC to pass compilation.
This patch remove the "select ATMEL_SSC" from SND_ATMEL_SOC_SSC to avoid above
warnings. And then ensures all the machine drivers that select SND_ATMEL_SOC_SSC
need to depend on ATMEL_SSC.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
sv¾—