This reworks some of the SH7786 PCIe initialization code to dynamically
setup and size the various resource windows, as opposed to the original
code that simply wired in a couple of them statically.

At the same time, we tidy up the initialization code a bit, kill off some
read-only register twiddling that was gleaned from the bus analyzer, and
also propagate the physical slot/channel mapping.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>