It looks like boot ROM source code is not available [1], and looks for blobs during initialization [2]. This thread makes it sound like ARM is a complete write-off in this department. [3]

[1] https://community.nxp.com/t5/LPC-Microcontrollers/Where-may-...

[2] https://forums.puri.sm/t/the-i-mx8-cannot-be-deblobbed-nxp-s...

[3] https://www.reddit.com/r/ECE/comments/9oarto/arm_socs_with_o...