xbmc: Fix TexturePacker compile

Patch description:

use_texturepacker_native=yes

is needed because we obviously need a native-compiled binary, but the xbmc
build system does enable this variable only for darwin, android and
raspberry-pi targets.

USE_TEXTUREPACKER_NATIVE_ROOT="$(HOST_DIR)/usr"

is also needed because
USE_TEXTUREPACKER_NATIVE_ROOT="$TEXTUREPACKER_NATIVE_ROOT"
is only executed for raspberry-pi by xbmc/configure and only
USE_TEXTUREPACKER_NATIVE_ROOT is used by tools/TexturePacker/Makefile.in.

To sum up, building for raspberry-pi and other archs works out-of-the-box,
compiling for an Intel target, for example, fails:

In file included from SDL_anigif.cpp:23:0:
SDL_anigif.h:24:21: fatal error: SDL/SDL.h: No such file or directory
compilation terminated.
XBMCTex.cpp:34:21: fatal error: SDL/SDL.h: No such file or directory

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>