Do a major clean-up of the BUSDMA architecture. A large number of

Do a major clean-up of the BUSDMA architecture.  A large number of
essentially machine-independant drivers use the structures and definitions
in machine-dependant directories that are really machine-independant in
nature.

Split <machine/bus_dma.h> into machine-depdendant and machine-independant parts
and make the primary access run through <sys/bus_dma.h>.

Remove <machine/bus.h>, <machine/bus_memio.h> and <machine/bus_pio.h>.  The
optimizations related to bus_memio.h and bus_pio.h made a huge mess,
introduced machine-specific knowledge into essentially machine-independant
drivers, and required specific #include file orderings to do their job.
They may be reintroduced in some other form later on.

Move <machine/resource.h> to <sys/bus_resource.h>.  The contents of the file
is machine-independant or can be made a superset across many platforms.

Make <sys/bus.h> include <sys/bus_dma.h> and <sys/bus_resource.h> and
include <sys/bus.h> where necessary. Remove all #include's of
<machine/resource.h> and <machine/bus.h>.  That is, make the BUSDMA
infrastructure integral to I/O-mapped and memory-mapped accesses to devices
and remove a large chunk of machine-specific dependancies from drivers.
bus_if.h and device_if.h are now required to be present when using <sys/bus.h>.