There seems to be some symmetry between:
 - arch/x86/kernel/cpu/amd.c
 - arch/x86/kernel/cpu/intel.c

and:
 - arch/x86/kernel/cpu/microcode/amd.c
 - arch/x86/kernel/cpu/microcode/intel.c

The former files set the vendor_id field in the /proc/cpuinfo file,
while the latter files deal with microcode updates.

Hints for smarter detection are welcome!