[POWERPC] 85xx: Enable CONFIG_SERIAL_8250_SHARE_IRQ

On chip 8250 UARTs share an interrupts on existing 85xx processors.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/platforms/85xx/Kconfig

@@ -47,6 +47,7 @@ config MPC85xx
 	bool
 	select PPC_UDBG_16550
 	select PPC_INDIRECT_PCI
+	select SERIAL_8250_SHARE_IRQ if SERIAL_8250
 	default y if MPC8540_ADS || MPC85xx_CDS || MPC8560_ADS || MPC85xx_MDS
 
 config PPC_INDIRECT_PCI_BE