Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Rename busdma_sync() to busdma_sync_range() and rename the
base and size parameters to ofs and len (resp). Add a new
busdma_sync() that makes the entire MD coherent.

Change the dev argument from a full path to just the device
identification (e.g. isa:0x3f0 or pci0:2:1:0). In libbus,
the device is turned into a path name. For bus_space_map(),
the resource is now specified in a second argument.
Before:
bus.map('/dev/proto/pci0:2:1:0/pcicfg')
busdma.tag_create('/dev/proto/pci0:2:1:0/busdma', ...)
Now:
bus.map('pci0:2:1:0', 'pcicfg')
busdma.tag_create('pci0:2:1:0', ...)

Remove debugging output. We should have tracing instead.

Implement busdma_md_unload() and busdma_sync().

While here:
1. have the Python bindings contain constants for the space
identifiers and the sync operation.
2. change the segment iterators to return None when done,
not ENXIO.

Add busdma_md_create, busdma_md_destroy and busdma_md_load.

Free the segment objects properly.

Add accessor functions for iterating over segments. A segment
can be in bus address space, physical memory space or virtual
memory space.

Map the allocated DMA memory into the address space.

Add busdma_mem_alloc & busdma_mem_free.

Add DMA tag management to the C library and Python binding.