libhugetlbfs: not build obj32 for powerpc64

If obj32 needed, user can build lib32-libhugetlbfs.

Fix the below build issue for 64bit powerpc boards:
| fatal error: gnu/stubs-32.h: No such file or directory
|  # include <gnu/stubs-32.h>
|                            ^
| compilation terminated.
| make: *** [obj32/elflink.o] Error 1

Signed-off-by: Ting Liu <b28495@freescale.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>