xen/arm32: entry: Fold the macro SAVE_ALL in the macro vector

xen/arm32: entry: Fold the macro SAVE_ALL in the macro vector

Follow-up rework will require the macro vector to distinguish between
a trap from a guest vs while in the hypervisor.

The macro SAVE_ALL already has code to distinguish between the two and
it is only called by the vector macro. So fold the former into the
latter. This will help to avoid duplicating the check.

This is part of XSA-303.

Reported-by: Julien Grall <Julien.Grall@arm.com>
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>