core_timing: Convert core timing into a class

Gets rid of the largest set of mutable global state within the core.
This also paves a way for eliminating usages of GetInstance() on the
System class as a follow-up.

Note that no behavioral changes have been made, and this simply extracts
the functionality into a class. This also has the benefit of making
dependencies on the core timing functionality explicit within the
relevant interfaces.

src/core/hle/service/service.h

@@ -14,6 +14,14 @@
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 // Namespace Service
 
+namespace Core {
+class System;
+}
+
+namespace FileSys {
+class VfsFilesystem;
+}
+
 namespace Kernel {
 class ClientPort;
 class ServerPort;
@@ -21,10 +29,6 @@ class ServerSession;
 class HLERequestContext;
 } // namespace Kernel
 
-namespace FileSys {
-class VfsFilesystem;
-}
-
 namespace Service {
 
 namespace SM {
@@ -178,7 +182,8 @@ private:
 };
 
 /// Initialize ServiceManager
-void Init(std::shared_ptr<SM::ServiceManager>& sm, FileSys::VfsFilesystem& vfs);
+void Init(std::shared_ptr<SM::ServiceManager>& sm, Core::System& system,
+          FileSys::VfsFilesystem& vfs);
 
 /// Shutdown ServiceManager
 void Shutdown();