x86/PCI: refactor get_current_resources()

Rename get_current_resources() to probe_pci_root_info.

1. Remove resource list head from pci_root_info
2. Make get_current_resources() not pass resources
3. Rename get_current_resources() to probe_pci_root_info()

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>