[gas][aarch64] Turn on SVE when using f32mm or f64mm extensions

[Nick Clifton]

Hi Matthew,

> 2020-01-13  Matthew Malcomson  <matthew.malcomson@arm.com>
> 
> 	* config/tc-aarch64.c (f64mm, f32mm): Add sve as a feature
> 	dependency.

Approved - please apply.

Cheers
  Nick