The whole point of distro boot protocol is that is does not need to be detailed for the hikey, it is a generic protocol that means the user need not worry about any hikey specifics. The distro boot code gets the ramdisk load address from a u-boot environment variable and use this to load and boot the kernel. These environment variables are also documented in README.distro:
So, if you use the distro boot protocol to load the kernel, device tree and initramfs then there is no need for you to worry about the ramdisk load address. However if you are deliberately avoiding the distro boot protocol, you can also use the these environment variables to figure out safe load addresses for hikey.
You will need to provide some kernel boot arguments, but these are the same as when you boot debian so you should copy them from there... I don't have them to hand since all my scripts work by editing grub.cfg with scripts leaving the original arguments untouched.
Note you don't need anything like root=/dev/ram . When you boot the kernel with an initramfs then the ramdisk is mounted and entered regardless of the presence/absense/contents of the root= argument. In fact when you have an initramfs if is the initramfs rather than the kernel that becomes responsible for parsing root= and mounting an appropriate filesystem. So, if you have an initramfs that is the rootfs (so doesn't need to mount a rootfs) then the root= argument will be ignored.