Always make ofw_bus_if.h. While it's only used when option FDT is in the
kernel, it can always be generated. In theory we could omit it if option
FDT isn't present, but none of the rest of sys/modules does that. That
fine-grained control likely won't be reliable w/o a redesign of the
kernel/module config system.
Sponsored by: Netflix
and remove non-present symbols that are now reported by kmod_syms.awk.
Reviewed by: emaste
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D32878