ASoC: rt5682: Add the descriptions for the DMIC clock rate and delay settings

The patch adds the descriptions for the DMIC clock rate and delay settings.
Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Link: https://lore.kernel.org/r/20200323082547.7898-3-oder_chiou@realtek.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rt5682.txt

@@ -38,6 +38,12 @@ Optional properties:
 - clocks : phandle and clock specifier for codec MCLK.
 - clock-names : Clock name string for 'clocks' attribute, should be "mclk".
 
+- realtek,dmic-clk-rate-hz : Set the clock rate (hz) for the requirement of
+  the particular DMIC.
+
+- realtek,dmic-delay-ms : Set the delay time (ms) for the requirement of
+  the particular DMIC.
+
 Pins on the device (for linking into audio routes) for RT5682:
 
   * DMIC L1