boards: arm: gd32f450i_eval: enable pwm support

Enable timer1 and its pwm node. The board does not directly have any LED
connected to a PWM output. However, following the official
"TIMER_Breath_LED" example, user can bridge PB10 (TIMER1_CH2) to PE2
(LED1) to run quick samples such as samples/basic/blinky_pwm.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

boards/arm/gd32f450i_eval/doc/index.rst

@@ -68,6 +68,9 @@ The board configuration supports the following hardware features:
    * - NVIC
      - N/A
      - :dtcompatible:`arm,v7m-nvic`
+   * - PWM
+     - :kconfig:`CONFIG_PWM`
+     - :dtcompatible:`gd,gd32-pwm`
    * - SYSTICK
      - N/A
      - N/A

boards/arm/gd32f450i_eval/gd32f450i_eval-pinctrl.dtsi

@@ -17,4 +17,10 @@
 			pinmux = <DAC_OUT0_PA4>;
 		};
 	};
+
+	pwm1_default: pwm1_default {
+		group1 {
+			pinmux = <TIMER1_CH2_PB10>;
+		};
+	};
 };

boards/arm/gd32f450i_eval/gd32f450i_eval.dts

@@ -51,10 +51,20 @@
 		};
 	};
 
+	pwmleds {
+		compatible = "pwm-leds";
+
+		/* NOTE: bridge TIMER1_CH2 (PB10) and LED1 (PE2) */
+		pwm_led: pwm_led {
+			pwms = <&pwm1 2 PWM_POLARITY_NORMAL>;
+		};
+	};
+
 	aliases {
 		led0 = &led1;
 		led1 = &led2;
 		sw0 = &user_key;
+		pwm-led0 = &pwm_led;
 	};
 };
 
@@ -90,3 +100,13 @@
 	pinctrl-0 = <&dac_default>;
 	pinctrl-names = "default";
 };
+
+&timer1 {
+	status = "okay";
+
+	pwm1: pwm {
+		status = "okay";
+		pinctrl-0 = <&pwm1_default>;
+		pinctrl-names = "default";
+	};
+};

boards/arm/gd32f450i_eval/gd32f450i_eval.yaml

@@ -11,3 +11,5 @@ toolchain:
   - zephyr
   - gnuarmemb
   - xtools
+supported:
+  - pwm