Hi,
I assume you're trying to activate the TZASC of the i.mx6. I've had some issues with this myself. In the end I never really managed to make it work using the IOMUX (it also stopped executing when I tried to change the Gpr9 register) but it's possible to enable it using fuse programming. If you are actually trying to enable the TZASC and are willing to blow a fuse to do so you can execute "fuse prog 0 6 0x10000000" in uboot.
and the fusemap in the imx6 reference manual for some more info on the command.
This will blow the fuse and automatically enable the TZASC each time you reset the board. I had to wait some time before my board really worked 100% after executing that command so keep that in mind if something funky happens right after blowing the fuse.