gpu: Rewrite GPU command list processing with DmaPusher class.

- More accurate impl., fixes Undertale (among other games).

src/video_core/engines/maxwell_dma.h

@@ -24,7 +24,7 @@ public:
     ~MaxwellDMA() = default;
 
     /// Write the value to the register identified by method.
-    void WriteReg(u32 method, u32 value);
+    void CallMethod(const GPU::MethodCall& method_call);
 
     struct Regs {
         static constexpr std::size_t NUM_REGS = 0x1D6;