ASoC: davinci-mcasp: Add rule to constrain the minimum period size

The minimum period size (in frames) must be not lower than the FIFO size
of McASP and in general too small period size would easily result underrun
in applications as eDMA - the most common DMA servicing McASP have support
for limited number of periods.

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