atsha204: go back from feeding entropy in preinit to init

Now we feed entropy as soon as possible but in init. The reason is because in preinit the kernel modules are not yet loaded and atsha204 requires I2C to communicate. This is loaded later on and thus can't be in preinit. It also makes sense to load it at the same as we other services providing the same functionality (such as haveged).

Fixes turris/turris-os-packages#725

Companion MR turris/turris-build!350