In this GRN, Marcel Moolenaar overhauled the logic for mounting
the root file system on bootup:

   |------------------------------------------------------------------------
   |r214006 | marcel | 2010-10-17 22:01:53 -0700 (Sun, 17 Oct 2010) | 20 lines
   |
   | Re-implement the root mount logic using a recursive approach, whereby each
   |root file system (starting with devfs and a synthesized configuration) can
   |contain directives for mounting another file system as root.
   |------------------------------------------------------------------------

This commit adds a mount.conf(8) man page which documents
the root mount logic.  mount.conf(8) also provides some examples
for the /.mount.conf file, which can be used to change the root mount behavior.

Reviewed by: marcel bjk
Add bus_dmamap_load_bio and bus_dmamap_load_ccb to bus_dma(9).

Sponsored by:	Intel
Reviewed by:	kib
MFC after:	3 days