PCI: Make early dump functionality generic

Move early dump functionality into common code so that it is available for
all architectures.  No need to carry arch-specific reads around as the read
hooks are already initialized by the time pci_setup_device() is getting
called during scan.

Tested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>