No need to keep the 32 bit space mapped, since it is only used by userland and through mmap; also shrink the softc of about 120 bytes by not keeping a copy of all prom regions when only two of them are needed.
No need to keep the 32 bit space mapped, since it is only used by userland
and through mmap; also shrink the softc of about 120 bytes by not keeping a
copy of all prom regions when only two of them are needed.

While there, map THC at the preferred address on S24 flavours, and do not
reprogram the control bits on S24 at attach time (since the prom has already
done this for us).

Tested on ss4 and ss5+S24.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars