Boot linux from QSPI on stm32f746g-disco

I've downloaded the pre-bulit linux image provided by emcraft to STM32F746G discovery board using u-boot. The QSPI entry address is 0x90000000. After downloading the image I wasn't able to boot linux using the bootm command. The syntax is simple: bootm 90000000. I got the following error:

Wrong image format for bootm command

Error: Can't get kernel image

Any help?

p.s.: I am able to download and boot the image from sdram using the same commands