We were building the omap-rng driver, because the same block is used
on some recent Marvell chips and HW_RANDOM_OMAP is enabled by default
if ARCH_MVEBU is enabled.
We were also building virtio-rng, but there isn't (so far as I know)
any publicly available emulation of the ARMv5 Marvell chips.
As we're about to include HWRNG drivers to the installer, disable the
whole subsystem for armel/marvell to avoid adding useless drivers.