arm64: dts: ti: k3-am68-sk: Add DT node for PCIe

AM68 Starter kit features with one PCIe M.2 Key M connector
interfaced via two SerDes lanes. Update the SerDes configuration
for PCIe.
Signed-off-by: Sinthu Raja <sinthu.raja@ti.com>
Signed-off-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Link: https://lore.kernel.org/r/20230921100039.19897-3-r-gunasekaran@ti.comSigned-off-by: Vignesh Raghavendra <vigneshr@ti.com>

arch/arm64/boot/dts/ti/k3-am68-sk-base-board.dts

@@ -553,3 +553,32 @@ dpi_out0: endpoint {
 		};
 	};
 };
+
+&serdes_ln_ctrl {
+	idle-states = <J721S2_SERDES0_LANE0_PCIE1_LANE0>, <J721S2_SERDES0_LANE1_PCIE1_LANE1>,
+		      <J721S2_SERDES0_LANE2_USB_SWAP>, <J721S2_SERDES0_LANE3_USB>;
+};
+
+&serdes_refclk {
+	clock-frequency = <100000000>;
+};
+
+&serdes0 {
+	status = "okay";
+
+	serdes0_pcie_link: phy@0 {
+		reg = <0>;
+		cdns,num-lanes = <2>;
+		#phy-cells = <0>;
+		cdns,phy-type = <PHY_TYPE_PCIE>;
+		resets = <&serdes_wiz0 1>, <&serdes_wiz0 2>;
+	};
+};
+
+&pcie1_rc {
+	status = "okay";
+	reset-gpios = <&exp1 10 GPIO_ACTIVE_HIGH>;
+	phys = <&serdes0_pcie_link>;
+	phy-names = "pcie-phy";
+	num-lanes = <2>;
+};