WITH[OUT]_SSP to avoid hitting an error if user has WITH_SSP in their
make.conf. Ports now use this knob.
make[7]: "/usr/src/share/mk/bsd.own.mk" line 466: WITH_SSP and
WITHOUT_SSP can't both be set.
This is similar to previous cleanup done in r188895
Approved by: bapt
Reviewed by: jlh (earlier version)
Approved by: re (marius)
MFC after: 1 week
It uses new API from the part.c to work with partition tables.
Update userboot's disk driver to use new API. Note that struct
loader_callbacks_v1 has changed.