[ARM] pxa: allow reuse of serial driver for pxa168

Signed-off-by: Eric Miao <eric.miao@marvell.com>

drivers/serial/Kconfig

@@ -628,7 +628,7 @@ config SERIAL_MPSC_CONSOLE
 
 config SERIAL_PXA
 	bool "PXA serial port support"
-	depends on ARM && ARCH_PXA
+	depends on ARCH_PXA || ARCH_MMP
 	select SERIAL_CORE
 	help
 	  If you have a machine based on an Intel XScale PXA2xx CPU you