unicore32/PCI: Remove pci=firmware command line parameter handling

Remove support for the "pci=firmware" command line parameter, which was
way to keep the kernel from changing any PCI BAR assignments.  This was
copied from ARM, but is not actually needed on unicore32.

The corresponding ARM support was removed by 903589ca ("ARM: 8554/1:
kernel: pci: remove pci=firmware command line parameter handling").

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