Initialise the UBOOT variable by default. Otherwise it will be unintended inherit to following images if set and causes an uboot build where not required. Signed-off-by: Mathias Kresin <dev@kresin.me>
This is in preparation for adding a subtarget for the Cortex A53 later. Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>