Open window to bootROM memory on Armada38x to allow CPU1 to boot

CPU1 is halted in bootROM code while it is waiting to be released.
Memory window to bootROM must be opened before booting the core.

Obtained from: Semihalf
Sponsored by: Stormshield
Submitted by: Michal Stanek <mst@semihalf.com>
Differential revision: https://reviews.freebsd.org/D4425