[TF-A] Non volatile boot index for the purpose of firmware update

Hi I'm looking for a suggestion for a reliable place to store a small boot index for PSA Firmware Update. SNVS LPGPRs looked promising, but NXP’s guidance is thin and we don’t keep the battery-backed LP domain alive, so those values won’t survive many power cycles. Are there better options on LS1028A? Would using the user RAM byte in our external I2C RTC make sense? Or perhaps should I store it on eMMC? (we don't use raw NOR/NAND flash). That RTC I mentioned is already accessed in both U-Boot and Linux, so I’m wary of conflicts but can try it if you think it’s viable. Any suggestions would be much appreciated.

Best regards Patryk