pci: typedef pcibus_t as uint64_t instead of uint32_t.

This patch is preliminary for 64bit bar.
For 64bit bar support, change pcibus_t which represents
pci bus addr/size from uint32_t to uint64_t.
And also change FMT_pcibus for printf.

In pci_update_mapping() checks 32bit overflow.
So the check must be updated too.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
