uboot-imx

bcm281xx: boot0 hook: adjust to unified boot0 semantics

This updates the BCM281xx boot0-hook to the updated boot0 semantics
by emitting _start and the vector table before the boot0 hook (as
was the case before).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>