pci: implement pci bridge filtering.

pci: implement pci bridge filtering.

This patch implements pci bridge filtering.

TODO: currently almost all the map funcions assumes
filtered_size == size and addr & ~(size - 1) == addr.
However with bridge filtering, they aren't always true.
Teach them such cases, such that filtered_size < size and
addr & (size - 1) != 0.

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