linux/common-config: Enable PWM support

Necessary to support the backlight on the GPD Pocket, GPD Win and several other devices.

pkgs/os-specific/linux/kernel/common-config.nix

@@ -126,6 +126,9 @@ let
       # GPIO power management
       POWER_RESET_GPIO                 = option yes;
       POWER_RESET_GPIO_RESTART         = option yes;
+
+      # Enable Pulse-Width-Modulation support, commonly used for fan and backlight.
+      PWM                              = yes;
     } // optionalAttrs (stdenv.hostPlatform.isx86) {
       INTEL_IDLE                       = yes;
       INTEL_RAPL                       = whenAtLeast "5.3" module;