arch/powerpc: add powerpc64le support

Technically, I don't forbid powerpcle support either, but I'm not sure that
there is any library/compiler support for that at the moment (though the hw
technically makes it possible).

powerpc64le needs glibc 2.19 and gcc 4.9. I haven't looked into the support
tools, but at least gdb 7.5 is too old (7.7.1 definitely has support).

Also make powerpc64 non-experimental. It's practically old at this point.

Signed-off-by: Cody P Schafer <dev@codyps.com>
[yann.morin.1998@free.fr: use ${target_endian_le} and ${target_bits_64}]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <64bfbbced9dd8f62e0d6.1399801945@gun>
Patchwork-Id: 347775

 diff -durN gcc-4.4.0.orig/include/libiberty.h gcc-4.4.0/include/libiberty.h

 --- gcc-4.4.0.orig/include/libiberty.h	2008-06-24 03:42:31.000000000 +0200

 +++ gcc-4.4.0/include/libiberty.h	2009-05-27 21:38:24.000000000 +0200

 @@ -595,8 +595,11 @@

  /* Like sprintf but provides a pointer to malloc'd storage, which must

     be freed by the caller.  */

 +/* asprintf may be declared as a macro by glibc with __USE_FORTIFY_LEVEL.  */

 +#ifndef asprintf

  extern int asprintf (char **, const char *, ...) ATTRIBUTE_PRINTF_2;

  #endif

 +#endif

  #if !HAVE_DECL_VASPRINTF

  /* Like vsprintf but provides a pointer to malloc'd storage, which