ntb: Use uintmax_t casts and %j to print physical addresses.

This fixes -Wint-to-pointer-cast errors with GCC when compiling on
i386 where physical addresses are not the same size as pointers.

Reviewed by: mav, imp
Differential Revision: https://reviews.freebsd.org/D36751

(cherry picked from commit 124e46735e07037afafbf0caa097faafb09c7329)