So, wouldn't we need a small, architecture-independent, infrastructure,
through which architecture-specific code could "register" at boot
time which SoC we are running on, and drivers could query this
information from the common infrastructure?

Of course, the major problem is to figure out what is the good
representation for this SoC identifier. Do we need a big list of SoCs
like we had machine IDs? A simple string? Or maybe there is just no
good way, and the whole idea is moot.

I did think about stuffing it inside the cpuinfo structures:

$ cat /proc/cpuinfo 
Processor       : Feroceon 88FR131 rev 1 (v5l)
BogoMIPS        : 1196.85
Features        : swp half thumb fastmult edsp 
CPU implementer : 0x56
CPU architecture: 5TE
CPU variant     : 0x2
CPU part        : 0x131
CPU revision    : 1

Hardware        : BUBBA3 Kirkwood based miniserver
Revision        : 0000
Serial          : 0000000000000000

I could imaging a 
SoC             : MV88F6281

It would probably need a bit of string parsing by any consumer, which
is not so good.

   Andrew