pwm: mediatek: add pwm support for MediaTek MT7987 SoC

This patch adds pwm support for MediaTek MT7987 SoC.

diff --git a/arch/arm/dts/mt7987a.dtsi b/arch/arm/dts/mt7987a.dtsi
index 028f563..bf53e89 100644
--- a/arch/arm/dts/mt7987a.dtsi
+++ b/arch/arm/dts/mt7987a.dtsi
@@ -59,6 +59,8 @@
 };
 
 &pwm {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pwm_pins>;
 	status = "okay";
 };