Refactor NDS and DSi to be objects (#1893)

* First crack at refactoring NDS and DSi into objects

- Remove all global/`static` variables in `NDS` and related classes
- Rely more on virtual dispatch when we need to pick methods at runtime
- Pass `NDS&` or `DSi&` to its constituent components where necessary
- Introduce some headers or move some definitions to break `#include` cycles

* Refactor the frontend to accommodate the core's changes

* Move up `SchedList`'s declaration

- Move it to before the components are initialized so the `map`s inside are initialized
- Fields in C++ are initialized in the order they're declared

* Fix a crash when allocating memory

* Fix JIT-free builds

* Fix GDB-free builds

* Fix Linux builds

- Explicitly qualify some member types in NDS, since they share the same name as their classes

* Remove an unnecessary template argument

- This was causing the build to fail on macOS

* Fix ARM and Android builds

* Rename `Constants.h` to `MemConstants.h`

* Add `NDS::IsRunning()`

* Use an `#include` guard instead of `#pragma once`

src/SPI.h

@@ -42,11 +42,11 @@ enum
 u16 CRC16(const u8* data, u32 len, u32 start);
 
 class SPIHost;
-
+class NDS;
 class SPIDevice
 {
 public:
-    SPIDevice(SPIHost* host) : Host(host), Hold(false), DataPos(0) {}
+    SPIDevice(melonDS::NDS& nds) : NDS(nds), Hold(false), DataPos(0) {}
     virtual ~SPIDevice() {}
     virtual void Reset() = 0;
     virtual void DoSavestate(Savestate* file) = 0;
@@ -56,7 +56,7 @@ public:
     virtual void Release() { Hold = false; DataPos = 0; }
 
 protected:
-    SPIHost* Host;
+    melonDS::NDS& NDS;
 
     bool Hold;
     u32 DataPos;
@@ -66,12 +66,12 @@ protected:
 class FirmwareMem : public SPIDevice
 {
 public:
-    FirmwareMem(SPIHost* host);
+    FirmwareMem(melonDS::NDS& nds);
     ~FirmwareMem() override;
     void Reset() override;
     void DoSavestate(Savestate* file) override;
 
-    void SetupDirectBoot(bool dsi);
+    void SetupDirectBoot();
 
     const class Firmware* GetFirmware();
     bool IsLoadedFirmwareBuiltIn();
@@ -96,7 +96,7 @@ private:
 class PowerMan : public SPIDevice
 {
 public:
-    PowerMan(SPIHost* host);
+    PowerMan(melonDS::NDS& nds);
     ~PowerMan() override;
     void Reset() override;
     void DoSavestate(Savestate* file) override;
@@ -116,7 +116,7 @@ private:
 class TSC : public SPIDevice
 {
 public:
-    TSC(SPIHost* host);
+    TSC(melonDS::NDS& nds);
     virtual ~TSC() override;
     virtual void Reset() override;
     virtual void DoSavestate(Savestate* file) override;
@@ -141,7 +141,7 @@ protected:
 class SPIHost
 {
 public:
-    SPIHost();
+    SPIHost(melonDS::NDS& nds);
     ~SPIHost();
     void Reset();
     void DoSavestate(Savestate* file);
@@ -161,6 +161,7 @@ public:
     void TransferDone(u32 param);
 
 private:
+    melonDS::NDS& NDS;
     u16 Cnt;
 
     SPIDevice* Devices[3];