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

 --- a/bfd/elf32-arm.c

 +++ b/bfd/elf32-arm.c

 @@ -12408,7 +12408,8 @@ elf32_arm_check_relocs (bfd *abfd, struc

  	  /* If the symbol is a function that doesn't bind locally,

  	     this relocation will need a PLT entry.  */

 -	  root_plt->refcount += 1;

 +	  if (root_plt->refcount != -1)

 +	    root_plt->refcount += 1;

  	  if (!call_reloc_p)

  	    arm_plt->noncall_refcount++;