Separate pciinit.c into clearly delineated sections.

Separate pciinit.c into clearly delineated sections.

There are four separate phases of the current PCI initialization code:
bus initialization, bus sizing, bar allocation, and misc device init.
Move the code exclusively called in each phase next to each other, and
clearly mark each section.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>