sysclk: code cleanup and fan speed

also fix incompatibility with nx fancontrol

Source/sys-clk/common/include/rgltr_services.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <switch.h>  // for Service, Result, hosversionBefore(), smGetService(), serviceClose(), etc.
+#include "rgltr.h"   // for RgltrSession, PowerDomainId, etc.
+
+extern Service g_rgltrSrv;
+
+Result rgltrInitialize(void);
+void   rgltrExit(void);
+
+Result rgltrOpenSession(RgltrSession* session_out, PowerDomainId module_id);
+
+Result rgltrGetVoltage(RgltrSession* session, u32* out_volt);
+
+void   rgltrCloseSession(RgltrSession* session);