[ARM] Add FP16 feature extension for ARMv8.2 architecture

[Nick Clifton]

Hi Jiong,

> 2016-02-16  Matthew Wahab  <matthew.wahab@arm.com>
>             Jiong Wang  <jiong.wang@arm.com>
> 
> 
> include/
>   * opcode/arm.h (ARM_EXT2_FP16_INSN): New.
> 
> gas/
>   * config/tc-arm.c (arm_ext_fp16): New.
>   (arm_extensions): New entry for "fp16".

Approved - please apply.

Cheers
  Nick