Remove condition which can never be true as the previous loop
is never exited while remote == NULL.

Reported by:	Coverity
Approved by:	bapt
MFC after:	2 days
Teach nexus(4) about Open Firmware (e.g. FDT) on ARM and MIPS, retiring
fdtbus in most cases. This brings ARM and MIPS more in line with existing
Open Firmware platforms like sparc64 and powerpc, as well as preventing
double-enumeration of the OF tree on embedded PowerPC (first through nexus,
then through fdtbus).

This change is also designed to simplify resource management on FDT platforms
by letting there exist a platform-defined root bus resource_activate() call
instead of replying on fdtbus to do the right thing through fdt_bs_tag.
The OFW_BUS_MAP_INTR() and OFW_BUS_CONFIG_INTR() kobj methods are also
available to implement for similar purposes.

Discussed on:	-arm, -mips
Tested by:	zbb, brooks, imp, and others
MFC after:	6 weeks