clang-modernize -use-nullptr

and s/\bNULL\b/nullptr/g for *.cpp/h/mm files not compiled on my machine

Source/DSPSpy/main_spy.cpp

@@ -51,7 +51,7 @@
 // Used for communications with the DSP, such as dumping registers etc.
 u16 dspbuffer[16 * 1024] __attribute__ ((aligned (0x4000)));
 
-static void *xfb = NULL;
+static void *xfb = nullptr;
 void (*reboot)() = (void(*)())0x80001800;
 GXRModeObj *rmode;
 
@@ -522,7 +522,7 @@ void InitGeneral()
 
 	// Obtain the preferred video mode from the system
 	// This will correspond to the settings in the Wii menu
-	rmode = VIDEO_GetPreferredMode(NULL);
+	rmode = VIDEO_GetPreferredMode(nullptr);
 
 	// Allocate memory for the display in the uncached region
 	xfb = MEM_K0_TO_K1(SYS_AllocateFramebuffer(rmode));