[bhnd] Add bhnd bridge support for bus_adjust_resource().

Adds support for adjusting active bus resource allocations, limiting the
range to the constraints of the register window within which the resource
is mapped.

This is the final set of bhnd changes required to support delegating
ChipCommon's register space to child devices.

Submitted by: Landon Fuller <landonf@landonf.org>
Differential Revision: https://reviews.freebsd.org/D6470