Mark geom classes as deprecated.
geom_bsd, geom_mbr and geom_sunlabel have been obsolete since Marcel
Moolenaar's geom_part was in FreeBSD 7. They haven't been in GENERIC
since FreeBSD 8. Add warning when used.
geom_vol_ffs has been obsolete since ufs support to geom_label was
committed in FreeBSD 5. It hasn't been in GENERIC since FreeBSD 5.
Add warning when used.
geom_fox has been obsolete since gmultipath was committed in FreeBSD 7.
(no warning added, since this is a very obscure class).
These will all be removed in FreeBSD 12.
MFC After 3 days
Differential Revision https://reviews.freebsd.org/D11935
Note Classes will be removed after MFC