use NULL dump segop as a shorthand for no-op
Instead of forcing every segment driver to implement a dummy function that
does nothing, handle NULL dump segop function pointer as a no-op shorthand.

*** 100,117 ****
  /*
   * Private seg op routines.
   */
  faultcode_t segkpm_fault(struct hat *hat, struct seg *seg, caddr_t addr,
                          size_t len, enum fault_type type, enum seg_rw rw);
- static void     segkpm_dump(struct seg *);
  static int      segkpm_pagelock(struct seg *seg, caddr_t addr, size_t len,
                          struct page ***page, enum lock_type type,
                          enum seg_rw rw);
  
  static const struct seg_ops segkpm_ops = {
          .fault          = segkpm_fault,
-         .dump           = segkpm_dump,
          .pagelock       = segkpm_pagelock,
  //#ifndef SEGKPM_SUPPORT
  #if 0
  #error FIXME: define nop
          .dup            = nop,
--- 100,115 ----
*** 316,329 ****
  segkpm_pagelock(struct seg *seg, caddr_t addr, size_t len,
          struct page ***page, enum lock_type type, enum seg_rw rw)
  {
          return (ENOTSUP);
  }
- 
- /*
-  * segkpm pages are not dumped, so we just return
-  */
- /*ARGSUSED*/
- static void
- segkpm_dump(struct seg *seg)
- {
- }
--- 314,318 ----