There is no reason for this to be #ifdef'd; but it should be conditional on this information not being otherwise available (which will always be the case on 64 bits), I would assume. If we are setting a value there, we should presumably also set 32 in the other case.
It does get set to 32 first (and only for 32-bits - 64bits didn't set any
default so far, so I didn't want to make it to now), and the code fragment
above updates that default after feature flags have been obtained, but
before other capabilities (including the phys/virt bit widths) are being
gathered.