N-Gage port: add changes from code reviews, overall cleanup (#5618)

* Add changes from code review by @ccawley2011, #5597, overall cleanup

* Update N-Gage README, minor cleanup and rephrasing

* Call SDL_SetMainReady() before calling SDL_main, return SDL_main instead of main

include/SDL_config_ngage.h

@@ -62,7 +62,7 @@ typedef unsigned long      uintptr_t;
 /* Enable the N-Gage timer support (src/timer/ngage/\*.c) */
 #define SDL_TIMER_NGAGE  1
 
-/* Enable the N=Hahe video driver (src/video/ngage/\*.c) */
+/* Enable the N-Gage video driver (src/video/ngage/\*.c) */
 #define SDL_VIDEO_DRIVER_NGAGE 1
 
 /* Enable the dummy audio driver (src/audio/dummy/\*.c) */