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 <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

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

···
 /* 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 */