powerpc/85xx: Add platform_device declaration to fsl_pci.h

mpc85xx_pci_err_probe(struct platform_device *op) need platform_device
declaration for definition. Otherwise, it will cause compile error if any
files including fsl_pci.h without declaration of platform_device.

Signed-off-by: Jia Hongtao <hongtao.jia@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>