Common/DebugInterface: Namespace code under the Common namespace

Gets more identifiers out of the global namespace and makes it more in
line with the rest of the (mostly) namespaced Common code.

Source/Core/Core/PowerPC/BreakPoints.cpp

@@ -226,7 +226,7 @@ bool MemChecks::OverlapsMemcheck(u32 address, u32 length) const
   });
 }
 
-bool TMemCheck::Action(DebugInterface* debug_interface, u32 value, u32 addr, bool write,
+bool TMemCheck::Action(Common::DebugInterface* debug_interface, u32 value, u32 addr, bool write,
                        size_t size, u32 pc)
 {
   if ((write && is_break_on_write) || (!write && is_break_on_read))

Source/Core/Core/PowerPC/BreakPoints.h

@@ -10,7 +10,10 @@
 
 #include "Common/CommonTypes.h"
 
+namespace Common
+{
 class DebugInterface;
+}
 
 struct TBreakPoint
 {
@@ -35,7 +38,8 @@ struct TMemCheck
   u32 num_hits = 0;
 
   // returns whether to break
-  bool Action(DebugInterface* dbg_interface, u32 value, u32 addr, bool write, size_t size, u32 pc);
+  bool Action(Common::DebugInterface* dbg_interface, u32 value, u32 addr, bool write, size_t size,
+              u32 pc);
 };
 
 // Code breakpoints.

Source/Core/Core/PowerPC/PPCSymbolDB.h

@@ -39,7 +39,7 @@ public:
   void LogFunctionCall(u32 addr);
 
 private:
-  DebugInterface* debugger;
+  Common::DebugInterface* debugger;
 };
 
 extern PPCSymbolDB g_symbolDB;