Fix SDL2main on PSP (#5076)

- Fix SDL2main on PSP
  SDL2main was not working for PSP, because it wasn't being activated and
  it wasn't unsetting the main. Besides that a debug screen being started
  was causing issues with joystick input and the sceKernelExitGame calli
  is no longer needed with the current PSPDEV SDK.
- Clean up imports in PSP main
- Set PSP GPU and user modes in main
- Fix exit callback in PSP main

src/main/psp/SDL_psp_main.c

@@ -7,11 +7,12 @@
 
 #include "SDL_main.h"
 #include <pspkernel.h>
-#include <pspdebug.h>
-#include <pspsdk.h>
 #include <pspthreadman.h>
 #include <stdlib.h>
-#include <stdio.h>
+
+#ifdef main
+    #undef main
+#endif
 
 /* If application's main() is redefined as SDL_main, and libSDLmain is
    linked, then this file will create the standard exit callback,
@@ -23,11 +24,12 @@
    PSP_MAIN_THREAD_STACK_SIZE, etc.
 */
 
-PSP_MODULE_INFO("SDL App", 0, 1, 1);
+PSP_MODULE_INFO("SDL App", 0, 1, 0);
+PSP_MAIN_THREAD_ATTR(THREAD_ATTR_VFPU | THREAD_ATTR_USER);
 
 int sdl_psp_exit_callback(int arg1, int arg2, void *common)
 {
-    exit(0);
+    sceKernelExitGame();
     return 0;
 }
 
@@ -53,12 +55,8 @@ int sdl_psp_setup_callbacks(void)
 
 int main(int argc, char *argv[])
 {
-    pspDebugScreenInit();
     sdl_psp_setup_callbacks();
 
-    /* Register sceKernelExitGame() to be called when we exit */
-    atexit(sceKernelExitGame);
-
     SDL_SetMainReady();
 
     (void)SDL_main(argc, argv);