hi,
dual parallel not dual stack.
you see Xilinx microUboot. For Zynq/ZynqMP Xilinx use some small Uboot which copies files to the flash. this microuboot need correct DDR and flash settings, which comes from FSBL, which you select for programming...or SDK use script version of the FSBL. This FSBL depends on your XSA file which depends on your PS Zynq IP setup which depends on your HW. Some of the HW comes from trenz (in your case only QSPI and DDR), all other periphery depends on your carrier....and your PS-PL design....
br
John