MLK-20142-1 ARM64: dts: use internal pll as pcie ref on 8mm ddr4 board

Since the 8mm ddr4 evk board is same to the -revb evk board.
Configure the pcie ref clk as the internal pll clock.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>

arch/arm64/boot/dts/freescale/fsl-imx8mm-ddr4-evk.dts

@@ -50,3 +50,13 @@
 &flexspi {
 	status = "disabled";
 };
+
+/*
+ * External OSC is used as PCIe REFCLK on RevC board.
+ * DDR4 board is same to the RevB board, configure
+ * PCIe REFCLK to internal PLL.
+ */
+&pcie0{
+	ext_osc = <0>;
+	status = "okay";
+};