Eliminate most kernel modules from loader.conf, they do not belong
there because they are not required to bootstrap FreeNAS, and are
slow due to limited access to hardware from loader.

Introduce a new rc.d script, earlykld, derived from /etc/rc.d/kld,
which loads certain important kernel modules that provides storage
access, potentionally useful for ix-fstab.

(cherry picked from commit f196867c7b942fb778d6c38b7541d73b6d0730ca)