Change zfs-dkms requirement

Version 2.2.0.3-20 of dkms in the EPEL/Fedora repositories added the
necessary patches to support ZoL, Therefore, the zfs-dkms requirement
on dkms is set to match that version or higher. This allows us to
drop the custom dkms build in the ZoL EPEL/Fedora repositories.

References:

https://bugzilla.redhat.com/show_bug.cgi?id=1023598

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1873