Refactor the GPU to be object-oriented (#1873)

* Refactor GPU3D to be an object

- Who has two thumbs and is the sworn enemy of global state? This guy!

* Refactor GPU itself to be an object

- Wow, it's used in a lot of places
- Also introduce a new `Melon` namespace for a few classes
- I expect other classes will be moved into `Melon` over time

* Change signature of Renderer3D::SetRenderSettings

- Make it noexcept, and its argument const

* Remove some stray whitespace

src/DMA.cpp

@@ -47,9 +47,10 @@ using Platform::LogLevel;
 // TODO: timings are nonseq when address is fixed/decrementing
 
 
-DMA::DMA(u32 cpu, u32 num) :
+DMA::DMA(u32 cpu, u32 num, Melon::GPU& gpu) :
     CPU(cpu),
-    Num(num)
+    Num(num),
+    GPU(gpu)
 {
     if (cpu == 0)
         CountMask = 0x001FFFFF;
@@ -142,7 +143,7 @@ void DMA::WriteCnt(u32 val)
         if ((StartMode & 0x7) == 0)
             Start();
         else if (StartMode == 0x07)
-            GPU3D::CheckFIFODMA();
+            GPU.GPU3D.CheckFIFODMA();
 
         if (StartMode==0x06 || StartMode==0x13)
             Log(LogLevel::Warn, "UNIMPLEMENTED ARM%d DMA%d START MODE %02X, %08X->%08X\n", CPU?7:9, Num, StartMode, SrcAddr, DstAddr);
@@ -609,7 +610,7 @@ void DMA::Run9()
             NDS::ResumeCPU(0, 1<<Num);
 
             if (StartMode == 0x07)
-                GPU3D::CheckFIFODMA();
+                GPU.GPU3D.CheckFIFODMA();
         }
 
         return;