85xx: Move to a common linker script

There are really no differences between all the 85xx linker scripts so
we can just move to a single common one.  Board code is still able to
override the common one if need be.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/cpu/mpc85xx/config.mk b/cpu/mpc85xx/config.mk
index 2da4d53..beb3514 100644
--- a/cpu/mpc85xx/config.mk
+++ b/cpu/mpc85xx/config.mk
@@ -25,3 +25,6 @@
 
 PLATFORM_CPPFLAGS += -ffixed-r2 -Wa,-me500 -msoft-float -mno-string
 PLATFORM_CPPFLAGS +=$(call cc-option,-mno-spe)
+
+# Use default linker script.  Board port can override in board/*/config.mk
+LDSCRIPT := $(SRCTREE)/cpu/mpc85xx/u-boot.lds