this commit allows to make a standalone u-boot for nsa310b.
While both first-stage and second-stage u-boot work fine if
installed to flash or loaded with kwboot,
I could not get stock u-boot nor bodhi's u-boot to chainload
any second stage u-boot (I also tried with dockstar's uboot
that works fine on this device if loaded with kwboot).
Signed-off-by: Alberto Bursi <alberto.bursi@outlook.it>
