[PATCH, aarch64] Add prefetch support

[Gopalasubramanian, Ganesh]

Please ignore the previous patch sent. The attachment was wrong.

> There's no point in the buffer or the sprintf.
> The text is short enough to repeat whole pattern in the array:

Updated the patch for the above suggestions.
make -k check RUNTESTFLAGS="execute.exp compile.exp dg.exp" passes.

Is it ok for upstream?

Regards
Ganesh
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