use NULL capable segop as a shorthand for no-capabilities
Instead of forcing every segment driver to implement a dummy "return 0"
function, handle NULL capable segop function pointer as "no copabilities
supported" shorthand.

*** 92,102 ****
                          size_t len, struct segkp_data *kpd, uint_t flags);
  static int      segkp_load(struct hat *hat, struct seg *seg, caddr_t vaddr,
                          size_t len, struct segkp_data *kpd, uint_t flags);
  static struct   segkp_data *segkp_find(struct seg *seg, caddr_t vaddr);
  static int      segkp_getmemid(struct seg *seg, caddr_t addr, memid_t *memidp);
- static int      segkp_capable(struct seg *seg, segcapability_t capability);
  
  /*
   * Lock used to protect the hash table(s) and caches.
   */
  static kmutex_t segkp_lock;
--- 92,101 ----
*** 145,155 ****
          .checkprot      = segkp_checkprot,
          .kluster        = segkp_kluster,
          .dump           = segkp_dump,
          .pagelock       = segkp_pagelock,
          .getmemid       = segkp_getmemid,
-         .capable        = segkp_capable,
  };
  
  
  static void segkpinit_mem_config(struct seg *);
  
--- 144,153 ----
*** 1368,1384 ****
  segkp_getmemid(struct seg *seg, caddr_t addr, memid_t *memidp)
  {
          return (ENODEV);
  }
  
- /*ARGSUSED*/
- static int
- segkp_capable(struct seg *seg, segcapability_t capability)
- {
-         return (0);
- }
- 
  #include <sys/mem_config.h>
  
  /*ARGSUSED*/
  static void
  segkp_mem_config_post_add(void *arg, pgcnt_t delta_pages)
--- 1366,1375 ----