pcib(4): Write window registers after resource adjustment

When adjusting resources we should write updated window base/limit into
the registers. Without this newly added address range won't be routed
through the bridge properly.

Use MIN()/MAX() against current window base/limit to not shrink it on
the other side if the window is shared by several resources.

Align passed resource start/end to the set window granularity to keep
it properly aligned. Currently this is mostly called by other bridges
having the same window alignment, but it may be change one day.

Reviewed by: jrtc27, jhb
MFC after: 1 week
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D31693