This refactors the code as it was getting very confusing; before FuSmbios was
reading both SMBIOS and the kernel-provided DT -- and various things were
injecting overrides in three different place. To properly support FDT remove
one layer of indirection.
This also lets us use the compatible strings to enable plugins specifying the
flag _REQUIRE_HWID -- which means we only load the plugin if it's got a chance
of working. e.g.
[aspeed,ast2500]
