[AArch64] Speed up linking speed by skipping unncessary TLS reloc type check

[Nick Clifton]

Hi Jiong,

> 2015-07-17  Jiong Wang  <jiong.wang@arm.com>
>
> bfd/
>    * elfnn-aarch64.c (IS_AARCH64_TLS_RELAX_RELOC): New.
>    (aarch64_can_relax_tls): Use the new IS_AARCH64_TLS_RELAX_RELOC.

Approved - please apply.

Cheers
   Nick