dt-bindings: phy: cadence-sierra: Add clock ID for derived reference clock

Add clock ID for Sierra derived reference clock.
Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211223060137.9252-15-sjakhade@cadence.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

include/dt-bindings/phy/phy-cadence.h

@@ -18,5 +18,6 @@
 /* Sierra */
 #define CDNS_SIERRA_PLL_CMNLC		0
 #define CDNS_SIERRA_PLL_CMNLC1		1
+#define CDNS_SIERRA_DERIVED_REFCLK	2
 
 #endif /* _DT_BINDINGS_CADENCE_SERDES_H */