dt-bindings: phy: Sierra: Add bindings for Sierra in TI's J721E

Add DT binding documentation for Sierra PHY IP used in TI's J721E
SoC.
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/phy/phy-cadence-sierra.txt

@@ -2,21 +2,24 @@ Cadence Sierra PHY
 -----------------------
 
 Required properties:
-- compatible:	cdns,sierra-phy-t0
-- clocks:	Must contain an entry in clock-names.
-		See ../clocks/clock-bindings.txt for details.
-- clock-names:	Must be "phy_clk"
+- compatible:	Must be "cdns,sierra-phy-t0" for Sierra in Cadence platform
+		Must be "ti,sierra-phy-t0" for Sierra in TI's J721E SoC.
 - resets:	Must contain an entry for each in reset-names.
 		See ../reset/reset.txt for details.
 - reset-names:	Must include "sierra_reset" and "sierra_apb".
 		"sierra_reset" must control the reset line to the PHY.
 		"sierra_apb" must control the reset line to the APB PHY
-		interface.
+		interface ("sierra_apb" is optional).
 - reg:		register range for the PHY.
 - #address-cells: Must be 1
 - #size-cells:	Must be 0
 
 Optional properties:
+- clocks:		Must contain an entry in clock-names.
+			See ../clocks/clock-bindings.txt for details.
+- clock-names:		Must contain "cmn_refclk_dig_div" and
+			"cmn_refclk1_dig_div" for configuring the frequency of
+			the clock to the lanes. "phy_clk" is deprecated.
 - cdns,autoconf:	A boolean property whose presence indicates that the
 			PHY registers will be configured by hardware. If not
 			present, all sub-node optional properties must be