Enable elf_backend_rela_normal for AArch64

Enable elf_backend_rela_normal for AArch64

  If we are generating non-relocatable object and --emit-relocs specified,
  aarch64 ld is actually generating wrong addend for rela entry when
  relocate against local symbol.

  for example, for simple testcase

  foo.c
  ===

  const char * const a = "foo";

  const char *
  foo ()
  {
    return a;
  }

  bar.c
  ===

  const char * const b = "bar";

  const char * bar ()
  {
    return b;
  }

  aarch64-none-linux-gnu-ld --emit-relocs -o x.o  foo.o bar.o
  aarch64-none-linux-gnu-readelf -r x.o

   ... R_AARCH64_ADR_PRE 0000000000400018 .rodata + 0
   ... R_AARCH64_ADD_ABS 0000000000400018 .rodata + 0
   ... R_AARCH64_ADR_PRE 0000000000400018 .rodata + 0
   ... R_AARCH64_ADD_ABS 0000000000400018 .rodata + 0

   while it should be:

   ... R_AARCH64_ADR_PRE 0000000000400018 .rodata + 0
   ... R_AARCH64_ADD_ABS 0000000000400018 .rodata + 0
   ... R_AARCH64_ADR_PRE 0000000000400018 .rodata + 10
   ... R_AARCH64_ADD_ABS 0000000000400018 .rodata + 10

   bfd generic code could actually handle this properly, but only when
   elf_backend_rela_normal set to '1'.

   this patch enable this and remove those target specific hack.

    bfd/
      * elfnn-aarch64.c (elf_backend_rela_normal): Set to 1.
      (elfNN_aarch64_relocate_section): Remove duplicated addend adjustment
      when info->relocatable be true.

    ld/testsuite/
      * ld-aarch64/emit-relocs-local-addend-bar.s: * New source file.
      * ld-aarch64/emit-relocs-local-addend-foo.s: * Likewise.
      * ld-aarch64/emit-relocs-local-addend.d: * New testcase.
      * ld-aarch64/local-addend-r.d: Likewise.