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

 This patch is courtesy of OpenEmbedded, by Khem Raj <raj.khem@gmail.com>

 http://cgit.openembedded.org/cgit.cgi/openembedded/commit/?id=b85b779688f0abc389e3c25d06b54de8b86385c1

 Index: ltrace-0.5.3/Makefile.in

 ===================================================================

 --- ltrace-0.5.3.orig/Makefile.in	2009-10-23 22:06:08.130304691 -0700

 +++ ltrace-0.5.3/Makefile.in	2009-10-23 22:06:53.160369614 -0700

 @@ -39,6 +39,8 @@ ltrace:		main.o libltrace.a

  libltrace.a: 	sysdeps/sysdep.o $(OBJ)

  		$(AR) rcv $@ $^

 +$(OBJ):		sysdeps/sysdep.o

 +

  sysdeps/sysdep.o: dummy

  		$(MAKE) -C sysdeps/$(OS)