lttng-modules: build as 64-bit kernel module on e6500

lttng-modules: build as 64-bit kernel module on e6500

   *e6500 is built with 32b rootfs/64b kernel, build asf as 64bit too.
   *Fix the below build issue on e6500 core:
   | DEBUG: Executing shell function do_make_scripts
   | make: Entering directory `.../tmp/sysroots/t4240qds/usr/src/kernel'
   | CC scripts/mod/empty.o | scripts/mod/empty.c:1:0: error: -mcmodel not supported in this configuration
   | make[2]: *** [scripts/mod/empty.o] Error 1
   | make[1]: *** [scripts/mod] Error 2
   | make: *** [scripts] Error 2

Signed-off-by: Chunrong Guo <B40290@freescale.com>