[ARM] Add support for ARMv8.1 command line option.

[Nicholas Clifton]

Hi Matthew,

> gas/
> 2015-05-21  Matthew Wahab  <matthew.wahab@arm.com>
>
>      * config/tc-arm.c (arm_archs): Add "armv8.1-a".
>      * doc/c-arm.texi (ARM Options, -march): Add "armv8.1-a".
>
> include/opcode
> 2015-05-21  Matthew Wahab  <matthew.wahab@arm.com>
>
>      * arm.h (FPU_ARCH_CRYPTO_NEON_VFP_ARMV8_1): New.
>      (ARM_ARCH_V8_1A): New.
>      (ARM_ARCH_V8_1A_FP): New.
>      (ARM_ARCH_V8_1A_SIMD): New.
>      (ARM_ARCH_V8_1A_CRYPTOV1): New.
>      (ARM_FEATURE_CORE): New.

Approved - please apply - but please add a mention of the support to the 
gas/NEWS file.

Cheers
   Nick