ASoC: SOF: add a helper to get topology configured bclk

Add helper function sof_dai_ssp_bclk() to get the BCLK frequency
configured by topology.

Reviewed-by: Bard Liao <bard.liao@intel.com>
Signed-off-by: Brent Lu <brent.lu@intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210625205042.65181-4-pierre-louis.bossart@linux.intel.com


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