Deal with rpi and pc differences better
The problems I know are:
init loads brcmfmac module unconditionally. I think we should use /etc/modules, and conditionalize that file in dockerfile, something like "COPY modules.$(ARCH) /etc/modules".
The storage code doesn't know what to do with /sda in the pc build. This is really part of a bigger question of policy around USB storage, and I'm opening a separate issue for that.