[U-Boot] [U-Boot,03/10] arm: add a separate stack for TPL

[Philipp Tomsich]

> TPL stack may different from SPL and sys stack, add support for
> separate one when the board defines it.
> 
> Signed-off-by: Kever Yang <kever.yang at rock-chips.com>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> Acked-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  arch/arm/lib/crt0.S | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>