Minimal change to build linuxkpi on architectures with physical addresses larger

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