boot: refactor battery checking to use new powctl apis

stratosphere/boot/source/boot_splash_screen.cpp

@@ -29,8 +29,8 @@ namespace ams::boot {
     }
 
     void ShowSplashScreen() {
-        const u32 boot_reason = GetBootReason();
-        if (boot_reason == 1 || boot_reason == 4) {
+        const auto boot_reason = GetBootReason();
+        if (boot_reason == spl::BootReason_AcOk || boot_reason == spl::BootReason_RtcAlarm2) {
             return;
         }
 
@@ -38,7 +38,7 @@ namespace ams::boot {
         {
             /* Splash screen is shown for 2 seconds. */
             ShowDisplay(SplashScreenX, SplashScreenY, SplashScreenW, SplashScreenH, SplashScreen);
-            svcSleepThread(2'000'000'000ul);
+            os::SleepThread(TimeSpan::FromSeconds(2));
         }
         FinalizeDisplay();
     }