feat(power): Add power domain config

* High level ZMK_POWER_DOMAINS for the feature.
* ZMK_POWER_DOMAINS_DYNAMIC_DEFAULT config setting
   to have various subsystems add their respective devices to
   the chosen `zmk,default-power-domain` on init.

app/Kconfig

@@ -323,22 +323,35 @@ config ZMK_IDLE_TIMEOUT
 config ZMK_SLEEP
     bool "Enable deep sleep support"
     imply USB
-
-if ZMK_SLEEP
-
-config PM_DEVICE
-    default y
+    select PM_DEVICE
 
 config ZMK_IDLE_SLEEP_TIMEOUT
     int "Milliseconds of inactivity before entering deep sleep"
+    depends on ZMK_SLEEP
     default 900000
 
-#ZMK_SLEEP
-endif
+config ZMK_POWER_DOMAINS
+    bool "Enable automatic power domain handling"
+    default n
+    select PM_DEVICE
+    select PM_DEVICE_POWER_DOMAIN
+    select PM_DEVICE_RUNTIME
+    select POWER_DOMAIN
+    select POWER_DOMAIN_GPIO
+
+config ZMK_POWER_DOMAINS_DYNAMIC_DEFAULT
+    bool "Enable assigning peripherals to the chosen default power domain"
+    default n
+    depends on ZMK_POWER_DOMAINS
+    select PM_DEVICE_POWER_DOMAIN_DYNAMIC
+
+# Default this to 2, the most common scenario for this for ZMK is RGB + OLED
+config PM_DEVICE_POWER_DOMAIN_DYNAMIC_NUM
+    default 2
 
 config ZMK_EXT_POWER
     bool "Enable support to control external power output"
-    default y
+    default y if !ZMK_POWER_DOMAINS
 
 #Power Management
 endmenu

app/src/display/main.c

@@ -7,6 +7,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/init.h>
 #include <zephyr/device.h>
+#include <zephyr/pm/device.h>
 #include <zephyr/pm/device_runtime.h>
 #include <zephyr/devicetree.h>
 
@@ -118,6 +119,19 @@ void initialize_display(struct k_work *work) {
         return;
     }
 
+#if IS_ENABLED(CONFIG_ZMK_POWER_DOMAINS) && DT_HAS_CHOSEN(zmk_default_power_domain)
+
+    pm_device_runtime_enable(display);
+    if (!pm_device_on_power_domain(display)) {
+        int rc =
+            pm_device_power_domain_add(display, DEVICE_DT_GET(DT_CHOSEN(zmk_default_power_domain)));
+        if (rc < 0) {
+            LOG_ERR("Failed to add the display to the default power domain (0x%02x)", -rc);
+        }
+    }
+
+#endif
+
     initialized = true;
 
     initialize_theme();

app/src/rgb_underglow.c

@@ -7,6 +7,7 @@
 #include <zephyr/device.h>
 #include <zephyr/init.h>
 #include <zephyr/kernel.h>
+#include <zephyr/pm/device.h>
 #include <zephyr/pm/device_runtime.h>
 #include <zephyr/settings/settings.h>
 
@@ -250,6 +251,19 @@ static int zmk_rgb_underglow_init(const struct device *_arg) {
     }
 #endif
 
+#if IS_ENABLED(CONFIG_ZMK_POWER_DOMAINS) && DT_HAS_CHOSEN(zmk_default_power_domain)
+
+    pm_device_runtime_enable(led_strip);
+    if (!pm_device_on_power_domain(led_strip)) {
+        int rc = pm_device_power_domain_add(led_strip,
+                                            DEVICE_DT_GET(DT_CHOSEN(zmk_default_power_domain)));
+        if (rc < 0) {
+            LOG_ERR("Failed to add the LED strip to the default power domain (0x%02x)", -rc);
+        }
+    }
+
+#endif
+
     state = (struct rgb_underglow_state){
         color : {
             h : CONFIG_ZMK_RGB_UNDERGLOW_HUE_START,