amd64: restore semantic for VIRT_IN_DMAP()

[kib]

Summary

The macro should check if the virtual address falls into working direct
map, not that it falls into KVA potentially belonging to DMAP.  This was
its previous meaning, as can be seen in the only use by DMAP_TO_PHYS().

Fixes:  4dd828c80828637452a8a4e07a64e294c82e5d8b