Virtio RNG support (CONFIG_DRIVERS_VIRTIO_RNG=y) selects
CONFIG_ARCH_HAVE_RNG. On the other hand, if CONFIG_DEV_URANDOM=y,
it defaults to CONFIG_DEV_URANDOM_ARCH if CONFIG_ARCH_HAVE_RNG=y.
DEV_URANDOM_ARCH definition states that the implementation of the
/dev/urandom should be provided by the architecture-specifig logic,
including the function devurandom_register(). In this case, the
/dev/urandom may refer to the same driver as /dev/random that is
provided by the Virtio RNG driver, which is implemented by this
commit.
6b1be7c66c