[PATCH 1/3][Binutils] aarch64: Add support for GCS extension.

[Nick Clifton]

Hi Srinath,
> This patch adds for Guarded Control Stack Extension (GCS) extension. GCS feature is
> optional from Armv9.4-A architecture and enabled by passing +gcs option to -march
> (eg: -march=armv9.4-a+gcs) or using ".arch_extension gcs" directive in the assembly file.
> 
> Also this patch adds support for GCS instructions gcspushx, gcspopcx, gcspopx,
> gcsss1, gcsss2, gcspushm, gcspopm, gcsstr and gcssttr.
> 
> For this feature in gas/doc/c-aarch64.texi: column 2 is marked N/A, as this column
> "minimum architecture" is not relevant any more and will be removed in the later patches.
> 
> Regression tested for aarch64-none-elf target and found no regressions.
> 
> Ok for binutils-master?

Approved - please apply.

Cheers
   Nick