xen/arm64: entry: Introduce a macro to generate guest vector and use it

xen/arm64: entry: Introduce a macro to generate guest vector and use it

Most of the guest vectors are using the same pattern. This makes fairly
tedious to alter the pattern and risk introducing mistakes when updating
each path.

A new macro is introduced to generate the guest vectors and now use it
in the one that use the open-code version.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Juergen Gross <jgross@suse.com>