ASoC: make clock direction configurable in asoc-simple

Some CPU drivers (e. g. davinci-mcasp) may require the system clock to
be configured as OUT, while there's no good way currently to set
SND_SOC_CLK_OUT in simple-soc driver if the clock is fixed-rate.

This patch makes asoc_simple_card_init_dai() initialize clock to
SND_SOCK_CLK_OUT if explicitly stated in the relevant dts file. This
change is transparent and doesn't change the default behavior.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Mark Brown <broonie@kernel.org>