Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Rename bus_space to bus (i.e. drop _space). This makes the
API match the convenience macros in <sys/bus.h>. Bus space
can now reference both bus and busdma.

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

Add a C libary and a Python module that implements an API similar
to bus_space(9) and that uses the proto(4) driver for talking to
hardware. If the I/O resource is a memory mapped I/O resource,
then mmap(2) will be attempted to avoid read(2)/write(2) overhead.

Sponsored by: Juniper Networks, Inc.