LU-10086 libcfs: use dynamic minors for /dev/{lnet,obd}

Request dynamic minor allocation when registering /dev/lnet and
/dev/obd. Remove the obsolete create-device-if-not-found code from
register_ioc_dev().

Lustre-change: https://review.whamcloud.com/29741


Lustre-commit: e446c166

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I59c70912b4729f58a76dc6107b3e1d7379c6d7a3
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Signed-off-by: Minh Diep <minh.diep@intel.com>
Reviewed-on: https://review.whamcloud.com/29945


Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>