Minimal change to build linuxkpi on architectures with physical addresses larger
than virtual

Summary:
Some architectures have physical/bus addresses that are much larger
than virtual addresses. This change just quiets a warning, as DMAP is not used
on those architectures, and on 64-bit platforms uintptr_t is the same size as
vm_paddr_t and void *.

Reviewed By: hselasky
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D14043