Now that BCM283x source are buildable with SMP option it cam be moved to
GENERIC SMP config. SMP itself does not work on RPi3 yet due to lack of
PSCI monitor which is work in progress at the moment
Policy for FreeBSD/arm64 kernel config is the same one as for x86
architectures: provide GENERIC kernel bootable on as many systems
as possible. Since there is no SMP support for RPi 3 yet new kernel
config was introduced: GENERIC-UP, which is effectively GENERIC with
SMP option disabled