asoc: ext-clk: Add support for configuring ext clk

In the case an external clock is used to source the MCLK, configure
additional clock attributes to be sent to the DSP. Introduce parsing of
new DT properties about the external clock frequency which is required
to find the appropriate clock attributes whilst providing backward
compatibility to not send any additional clock attributes to the DSP.

Change-Id: I029080fe509f9545fb9785bf4a9225e9bb7dff46
Signed-off-by: Abhilash Sathyanarayana <quic_abhisath@quicinc.com>