Initial maemo platform support

Adds Nokia N900, N810 and N800 support.

Features:
- Introduce maemo specific platform defines
- Play audio in silent mode
- Stop playback on incoming calls
- Battery level readout
- Bluetooth headset support
- Save CPU by disabling screen updates if the display
  is off or the app doesn't have input focus
- N900: GStreamer audio backend

Kudos to kugel for the code review.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29248 a1c6a512-1295-4272-9138-f99709370657

apps/main.c

@@ -125,7 +125,7 @@
 #define MAIN_NORETURN_ATTR
 #endif
 
-#if (CONFIG_PLATFORM & PLATFORM_SDL)
+#if (CONFIG_PLATFORM & (PLATFORM_SDL|PLATFORM_MAEMO))
 #include "sim_tasks.h"
 #include "system-sdl.h"
 #define HAVE_ARGV_MAIN
@@ -351,7 +351,7 @@ static void init(void)
     show_logo();
     button_init();
     backlight_init();
-#if (CONFIG_PLATFORM & PLATFORM_SDL)
+#if (CONFIG_PLATFORM & (PLATFORM_SDL|PLATFORM_MAEMO))
     sim_tasks_init();
 #endif
 #if (CONFIG_PLATFORM & PLATFORM_ANDROID)