ppc4xx: Rework of 4xx serial driver (2)

Change all linker scripts to reference the changed driver name 4xx_uart.o.

Note: In most cased all these explicit referencing of these object files
in the linker scripts is not neccessary. Only for manually embedded
environment into the U-Boot image, which is not done is most cases.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/board/mpl/pip405/u-boot.lds b/board/mpl/pip405/u-boot.lds
index 11819a4..685f903 100644
--- a/board/mpl/pip405/u-boot.lds
+++ b/board/mpl/pip405/u-boot.lds
@@ -66,7 +66,7 @@
     cpu/ppc4xx/kgdb.o	(.text)
     cpu/ppc4xx/traps.o	(.text)
     cpu/ppc4xx/interrupts.o	(.text)
-    cpu/ppc4xx/serial.o	(.text)
+    cpu/ppc4xx/4xx_uart.o	(.text)
     cpu/ppc4xx/cpu_init.o	(.text)
     cpu/ppc4xx/speed.o	(.text)
     common/dlmalloc.o	(.text)