soundwire: add new mclk_freq field for properties

To help pass platform-specific values, add a new field that can either
be set by the Master driver or read from firmware (BIOS/DT).

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190806005522.22642-11-pierre-louis.bossart@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>