core/loader: Remove dependencies on the global system instance

Now all that remains is:

18 instances in file_sys code
14 instances in GDB stub code (this can be tossed wholesale)
4 instances in HLE code
2 instances in settings code.

src/core/loader/xci.h

@@ -9,6 +9,10 @@
 #include "core/file_sys/vfs.h"
 #include "core/loader/loader.h"
 
+namespace Core {
+class System;
+}
+
 namespace FileSys {
 class NACP;
 class XCI;
@@ -35,7 +39,7 @@ public:
         return IdentifyType(file);
     }
 
-    LoadResult Load(Kernel::Process& process) override;
+    LoadResult Load(Kernel::Process& process, Core::System& system) override;
 
     ResultStatus ReadRomFS(FileSys::VirtualFile& file) override;
     u64 ReadRomFSIVFCOffset() const override;