Move stuff from prebuilt to prebuilts/tools

Change-Id: I4090d12fc173af3d11cd3e1a449425ed134c5aed
diff --git a/Makefile.common b/Makefile.common
index da3226e..77fd367 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -220,7 +220,7 @@
 
 ifneq ($(BUILD_SDL_FROM_SOURCES),true)
 
-    SDL_CONFIG ?= prebuilt/$(QEMU_HOST_TAG)/sdl/bin/sdl-config
+    SDL_CONFIG ?= prebuilts/tools/$(QEMU_HOST_TAG)/sdl/bin/sdl-config
     SDL_CFLAGS := $(shell $(SDL_CONFIG) --cflags)
 
     # We need to filter out the _GNU_SOURCE variable because it breaks recent