[AArch64] Support RAS extension for ARMv8 onwards.

[Nick Clifton]

Hi Matthew,

> gas/
> 2016-04-18  Matthew Wahab  <matthew.wahab@arm.com>
> 
>      * config/tc-aarch64.c (aarch64_features): Add "ras".
>      * doc/c-aarch64.texi (AArch64 Extensions): Add "ras".
>      * testsuite/gas/aarch64/armv8-ras-1.d: New.
>      * testsuite/gas/aarch64/armv8-ras-1.s: New.
>      * testsuite/gas/aarch64/illegal-ras-1.d: New.
>      * testsuite/gas/aarch64/illegal-ras-1.s: New.

Approved - please apply.

Cheers
  Nick