[lldb] [Process/FreeBSDRemote] Implement GetLoadedModuleFileSpec() and GetFileLoadAddress()

Copy the Linux implementation of GetLoadedModuleFileSpec()
and GetFileLoadAddress() into NativeProcessFreeBSD.  This does not seem
to change anything at the moment but reducing the differences between
the plugins should help us in the long term.

Differential Revision: https://reviews.llvm.org/D92314