ppc: amcc: Omit unneeded ns16550 CONFIG if using driver model

This comes from the device tree or a call to get_uart_clock().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/include/asm/ppc460ex_gt.h b/arch/powerpc/include/asm/ppc460ex_gt.h
index f41df0d..ea019aa 100644
--- a/arch/powerpc/include/asm/ppc460ex_gt.h
+++ b/arch/powerpc/include/asm/ppc460ex_gt.h
@@ -19,10 +19,12 @@
 /* Memory mapped registers */
 #define CONFIG_SYS_PERIPHERAL_BASE	0xef600000 /* Internal Peripherals */
 
+#ifndef CONFIG_DM_SERIAL
 #define CONFIG_SYS_NS16550_COM1	(CONFIG_SYS_PERIPHERAL_BASE + 0x0300)
 #define CONFIG_SYS_NS16550_COM2	(CONFIG_SYS_PERIPHERAL_BASE + 0x0400)
 #define CONFIG_SYS_NS16550_COM3	(CONFIG_SYS_PERIPHERAL_BASE + 0x0500)
 #define CONFIG_SYS_NS16550_COM4	(CONFIG_SYS_PERIPHERAL_BASE + 0x0600)
+#endif
 
 #define GPIO0_BASE		(CONFIG_SYS_PERIPHERAL_BASE + 0x0b00)
 #define GPIO1_BASE		(CONFIG_SYS_PERIPHERAL_BASE + 0x0c00)