fix(boards): Move ARM clock config to DTS.

app/boards/arm/planck/planck_rev6.dts

@@ -1,11 +1,12 @@
 /*
- * Copyright (c) 2017 I-SENSE group of ICCS
+ * Copyright (c) 2020 The ZMK Contributors
  *
  * SPDX-License-Identifier: MIT
  */
 
 /dts-v1/;
 #include <st/f3/stm32f303Xc.dtsi>
+#include <st/f3/stm32f303c(b-c)tx-pinctrl.dtsi>
 #include <dt-bindings/zmk/matrix_transform.h>
 
 / {
@@ -83,6 +84,8 @@ layout_2x2u_transform:
 };
 
 &usb {
+	pinctrl-0 = <&usb_dm_pa11 &usb_dp_pa12>;
+	pinctrl-names = "default";
 	status = "okay";
 	cdc_acm_uart: cdc_acm_uart {
 		compatible = "zephyr,cdc-acm-uart";
@@ -90,6 +93,26 @@ layout_2x2u_transform:
 	};
 };
 
+&clk_hse {
+	status = "okay";
+	clock-frequency = <DT_FREQ_M(8)>;
+};
+
+&pll {
+	prediv = <1>;
+	mul = <9>;
+	clocks = <&clk_hse>;
+	status = "okay";
+};
+
+&rcc {
+	clocks = <&pll>;
+	clock-frequency = <DT_FREQ_M(72)>;
+	ahb-prescaler = <1>;
+	apb1-prescaler = <2>;
+	apb2-prescaler = <1>;
+};
+
 &flash0 {
 	/*
 	 * For more information, see: