powerpc/85xx: fix Kconfig warning about missing 8250 dependency

The SERIAL_8250_EXTENDED option just enables access to other
less regularly used options, like SERIAL_8250_SHARE_IRQ.
Select it to get rid of this warning when selecting the child
option living underneath it.

  warning: (FSL_SOC_BOOKE && SERIAL_8250_RM9K) selects
  SERIAL_8250_SHARE_IRQ which has unmet direct dependencies
  (HAS_IOMEM && SERIAL_8250_EXTENDED)

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/platforms/85xx/Kconfig

@@ -6,6 +6,7 @@ menuconfig FSL_SOC_BOOKE
 	select MPIC
 	select PPC_PCI_CHOICE
 	select FSL_PCI if PCI
+	select SERIAL_8250_EXTENDED if SERIAL_8250
 	select SERIAL_8250_SHARE_IRQ if SERIAL_8250
 	default y