[GAS][ARM] Add support for Cortex-A78 and Cortex-A78AE

[Przemyslaw Wirkus]

> > OK for master branch ?
> 
> Approved.
> 
> > PS: I do not have write permission, can this be commited in my name if
> > approved please?
> 
> With luck you will soon have access, so please apply this patch as a test of
> that access.

commit 42c36b7366dcff8886d3c50ccf38b227ce4a4da2

> Cheers
>   Nick
>