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/sysdeps/linux-gnu/mipsel/trace.c

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

 --- ltrace-0.5.3.orig/sysdeps/linux-gnu/mipsel/trace.c	2009-10-23 23:15:59.822783128 -0700

 +++ ltrace-0.5.3/sysdeps/linux-gnu/mipsel/trace.c	2009-10-23 23:16:10.441268788 -0700

 @@ -127,7 +127,6 @@ gimme_arg(enum tof type, Process *proc, 

  			return ret;

  		} else {

  			// If we need this, I think we can look at [sp+16] for arg_num==4.

 -			CP;

  			return 0;

  		}

  	}