UEFI provides a protocol for accessing randomness. This is a good way to gather early entropy, especially when there's no driver for the RNG on the platform (as is the case on the Marvell Armada8k (MACCHIATObin) for now).
FreeBSD already has a way to pass entropy from the loader to the kernel: via loading a module with a special type. (I was searching for where the entropy_cache_name etc. variables are used for quite some time before realizing it works dynamically together with regular modules :D)
With a little modification to module.c, we can allow other parts of the code to load modules from anywhere (not just the FS), and use this in the EFI-specific code to load a synthetic module with the entropy.