PCI: Remove arch-specific IORESOURCE_ROM_SHADOW size from sysfs

When pci_create_sysfs_dev_files() created the "rom" sysfs file, it set the
sysfs file size to the actual size of a ROM BAR, or if there was no ROM BAR
but the platform provided a shadow copy in RAM, to 0x20000.  0x20000 is an
arch-specific length that should not be baked into the PCI core.

Every place that sets IORESOURCE_ROM_SHADOW also sets the size of the
PCI_ROM_RESOURCE, so use the resource length always.

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