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 -urN glibc-2.10.1-orig/manual/Makefile glibc-2.10.1/manual/Makefile

 --- glibc-2.10.1-orig/manual/Makefile 2006-01-07 22:43:47.000000000 -0800

 +++ glibc-2.10.1/manual/Makefile 2014-01-15 11:49:08.256982014 -0800

 @@ -232,7 +232,11 @@

  .PHONY: stubs

  stubs: $(objpfx)stubs

  endif

 -$(objpfx)stubs ../po/manual.pot $(objpfx)stamp%:

 +$(objpfx)stamp%:

 +	$(make-target-directory)

 +	touch $@

 +

 +$(objpfx)stubs ../po/manual.pot:

  	$(make-target-directory)

  	touch $@