x86/PCI: embed name into pci_root_info struct

We now keep the pci_root_info struct for the entire lifetime of the
host bridge, so just embed the name in the struct rather than
allocating it separately.

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