ASoC: Samsung: Added to support mono recording

The dma size will be changed by requested number of
channel(mono/stereo) from platform. For mono recording,
channels_min value should be 1.

Signed-off-by: Sangsu Park <sangsu4u.park@samsung.com>
Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>