So I have managed to install arch linux on the eMMC and its working well. As a note to others I was unable to get the UEFI to recognise either a GRUB or systemd-boot bootloader with an ESP. As a workaround I enable legacy (BIOS) boot options in the SCU menu. After doing this I was able to get it to work with an MBR/BIOS boot partition with GRUB. Hope that helps someone.
It took a bit of doing, but I have been able to install Arch on the eMMC using UEFI. I'm a novice at all ths, so I made a number of different mistakes along the way, but the one most pertinent to your situation may be that I initially had significant difficulty creating an EFI system parition that mkfs.fat would agree to format (it errored out saying the partition was too small even though at creation it was 513 Mb). I think it wasn't working because I was inadvertently using MBR. When I used gdisk to force GPT, things started working. Hope this helps.
