[PATCH][GAS] aarch64: Update AArch64 features command line options docs 2/2

[Przemyslaw Wirkus]

> Hi Przemyslaw
> 
> > 2021-09-20  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>
> >
> > 	* doc/c-aarch64.texi: Update docs.
> 
> Approved - please apply.

commit b18be12aeaa97deba5cf104459514fe16f5de249

> Cheers
>    Nick
>