Use a fake exception to exit early in case of memory breakpoints.

Change TMemCheck::Action to return whether to break rather than calling
PPCDebugInterface::BreakNow, as this simplified the implementation; then
remove said method, as that was its only caller.  One "interface" method
down, many to go...

Source/Core/Core/Debugger/PPCDebugInterface.cpp

@@ -169,11 +169,6 @@ void PPCDebugInterface::InsertBLR(unsigned int address, unsigned int value)
 	PowerPC::HostWrite_U32(value, address);
 }
 
-void PPCDebugInterface::BreakNow()
-{
-	CCPU::Break();
-}
-
 
 // =======================================================
 // Separate the blocks with colors.

Source/Core/Core/Debugger/PPCDebugInterface.h

@@ -39,7 +39,6 @@ public:
 	virtual unsigned int GetPC() override;
 	virtual void SetPC(unsigned int address) override;
 	virtual void Step() override {}
-	virtual void BreakNow() override;
 	virtual void RunToBreakpoint() override;
 	virtual void InsertBLR(unsigned int address, unsigned int value) override;
 	virtual int GetColor(unsigned int address) override;