kernel: Let the kernel handle all page table changes when switching processes

It will both change the page table in memory and notify the CPU about the change by itself. This way there is no need to call memory.SetCurrentPageTable() when kernel.setCurrentProcess() and the management is kept internally in the kernel

src/core/core.h

@@ -255,7 +255,7 @@ private:
     std::unique_ptr<Loader::AppLoader> app_loader;
 
     /// ARM11 CPU core
-    std::unique_ptr<ARM_Interface> cpu_core;
+    std::shared_ptr<ARM_Interface> cpu_core;
 
     /// DSP core
     std::unique_ptr<AudioCore::DspInterface> dsp_core;