ASoC: fsl_spdif: Add support for imx6sx platform

The one difference on imx6sx platform is that the root clock
is shared with ASRC module, so we add a new flags
"shared_root_clock" which means the root clock is not independent,
then we will not do the clk_set_rate and clk_round_rate to avoid
impact ASRC module usage.

As add a new flags, we include the soc specific data struct.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Nicolin Chen <nicoleotsuka@gmail.com>
Link: https://lore.kernel.org/r/7a343edd5f8487abad248a0b862f45fd95067751.1592376770.git.shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>