The definition of CONFIG_SPL_BOOTROM_SAVE is always a fixed
CONFIG_SPL_STACK + 4, while CONFIG_SPL_STACK is not constant. This
change will make it clear where the location is still, once
CONFIG_SPL_STACK moves to Kconfig.
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>