FreeBSD: disable edonr in zfs_mod_supported_feature()

Rather than conditionally compiling out the edonr code for FreeBSD
update zfs_mod_supported_feature() to indicate this feature is
unsupported. This ensures that all spa features are defined on
every platform, even if they are not supported.

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #11605
Issue #11468