aarch64: Remove the redundant setup_stack

Since we already have set up a stack above, there is no need to do it
again.
Also, in fact it's a bug: setup_stack expects the logical CPU ID in
w0, and here we always call it with w0 being 1.

Signed-off-by: Jaxson Han <jaxson.han@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>