PCI: Add devm_request_pci_bus_resources()

Several host bridge drivers iterate through the list of bridge windows to
request resources.  Several others don't request the window resources at
all.

Add a devm_request_pci_bus_resources() interface to make it easier for
drivers to request all the window resources.  Export to GPL modules (from
Arnd Bergmann <arnd@arndb.de>).

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>