[POWERPC] Remove redundant pci_read_irq_line() function for 85xx platform

Remove redundant pci_read_irq_line() function for 85xx CDS board.
This function has been realized in common ppc pci code.

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>