boot: refactor battery checking to use new powctl apis

libraries/libstratosphere/include/stratosphere/spl/spl_types.hpp

@@ -150,6 +150,15 @@ namespace ams::spl {
         };
     };
     static_assert(sizeof(BootReasonValue) == sizeof(u32), "BootReasonValue definition!");
+
+    enum BootReason {
+        BootReason_Unknown   = 0,
+        BootReason_AcOk      = 1,
+        BootReason_OnKey     = 2,
+        BootReason_RtcAlarm1 = 3,
+        BootReason_RtcAlarm2 = 4,
+    };
+
     #pragma pack(push, 1)
 
     struct AesKey {