Allow the armv6 kernel to be build with PHYSADDR undefined. The kernel
will now find the virtual to physical mapping for libkvm to use at
runtime. This makes PHYSADDR redundant, however keep it around to give
everyone a chance to update their libkvm.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273288 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f