pmap - Change pmap_map syntaxis

pmap - Change pmap_map syntaxis

* Change pmap_map syntaxis to take a pointer to vm_offset_t, so the vaddr is
  modified when memory is mapped.

* Hence also don't return the modified vaddr, but rather return the mapped
  memory.

* This unifies the syntax for the different platforms, as on amd64, pmap_map
  returned the mapped area, instead of the changed vaddr.

* Modify vm_page.c accordingly, and also set aside some memory that minidumps
  need.