Add support for devid and phys_path keys in vdev disk labels

This is foundational work for ZED.

Updates a leaf vdev's persistent device strings on Linux platform

* only applies for a dedicated leaf vdev (aka whole disk)
* updated during pool create|add|attach|import
* used for matching device matching during auto-{online,expand,replace}
* stored in a leaf disk config label (i.e. alongside 'path' NVP)
* can opt-out using env var ZFS_VDEV_DEVID_OPT_OUT=YES

Some examples:

    path: '/dev/sdb1'
    devid: 'scsi-350000394a8ca4fbc-part1'
    phys_path: 'pci-0000:04:00.0-sas-0x50000394a8ca4fbf-lun-0'

    path: '/dev/mapper/mpatha'
    devid: 'dm-uuid-mpath-35000c5006304de3f'

Signed-off-by: Don Brady <don.brady@intel.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2856
Closes #3978
Closes #4416

lib/libspl/include/devid.h

@@ -28,82 +28,5 @@
 #define	_LIBSPL_DEVID_H
 
 #include <sys/types.h>
-#include <stdlib.h>
-
-typedef int ddi_devid_t;
-
-typedef struct devid_nmlist {
-	char *devname;
-	dev_t dev;
-} devid_nmlist_t;
-
-static inline
-int
-devid_str_decode(
-    char *devidstr,
-    ddi_devid_t *retdevid,
-    char **retminor_name)
-{
-	abort();
-}
-
-static inline
-int
-devid_deviceid_to_nmlist(
-    char *search_path,
-    ddi_devid_t devid,
-    char *minor_name,
-    devid_nmlist_t **retlist)
-{
-	abort();
-}
-
-static inline
-void
-devid_str_free(char *str)
-{
-	abort();
-}
-
-static inline
-void
-devid_free(ddi_devid_t devid)
-{
-	abort();
-}
-
-static inline
-void
-devid_free_nmlist(devid_nmlist_t *list)
-{
-	abort();
-}
-
-static inline
-int
-devid_get(
-    int fd,
-    ddi_devid_t *retdevid)
-{
-	return (-1);
-}
-
-static inline
-int
-devid_get_minor_name(
-    int fd,
-    char **retminor_name)
-{
-	abort();
-}
-
-static inline
-char *
-devid_str_encode(
-    ddi_devid_t devid,
-    char *minor_name)
-{
-	abort();
-}
 
 #endif