sparc32/PCI/LEON: Converge device enable path

Most architectures turn on PCI_COMMAND_IO and PCI_COMMAND_MEMORY in
pci_enable_device() when a driver claims the device.  Sparc LEON did it in
pcibios_fixup_bus(), which is called during enumeration, before any drivers
are attached.

Implement pcibios_enable_device() for LEON so it will do the same as other
architectures.  This implementation is copied verbatim from sparc64.

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