MAINTAINERS: Include more PCI files

Add more PCI files to the PCI subsystem.

I expect Rafael to continue merging things in drivers/acpi/pci*, but it's
nice to have linux-pci included on patches.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>