dracut: skip zfsexpandknoweldge when zfs_devs is present in dracut

PR 1711 (https://github.com/dracutdevs/dracut/pull/1711) adds a zfs_devs
function to dracut to detect the physical devices backing zfs pools. If
this function exists in the version of dracut this module is being
called from, then it does not need to run.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Savyasachee Jha <hi@savyasacheejha.com>
Closes #13121