MFC 221220:

MFC 221220:
Extend the rman(9) API to support altering an existing resource.
Specifically, these changes allow a resource to back a relocatable and
resizable resource such as the I/O window decoders in PCI-PCI bridges.
- rman_adjust_resource() can adjust the start and end address of an
  existing resource.  It only succeeds if the newly requested address
  space is already free.  It also supports shrinking a resource in
  which case the freed space will be marked unallocated in the rman.
- rman_first_free_region() and rman_last_free_region() return the
  start and end addresses for the first or last unallocated region in
  an rman, respectively.  This can be used to determine by how much
  the resource backing an rman must be adjusted to accomodate an
  allocation request that does not fit into the existing rman.

While here, document the rm_start and rm_end fields in struct rman,
rman_is_region_manager(), the bound argument to
rman_reserve_resource_bound(), and rman_init_from_resource().

git-svn-id: svn://svn.freebsd.org/base/stable/8@223501 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f