powerpc: MPC8555CDS: Remove macro CONFIG_MPC8555CDS

Use CONFIG_TARGET_MPC8555CDS instead.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/freescale/common/Makefile b/board/freescale/common/Makefile
index e01df42..06ce311 100644
--- a/board/freescale/common/Makefile
+++ b/board/freescale/common/Makefile
@@ -47,7 +47,7 @@
 
 obj-$(CONFIG_TARGET_MPC8541CDS)	+= cds_pci_ft.o
 obj-$(CONFIG_TARGET_MPC8548CDS)	+= cds_pci_ft.o
-obj-$(CONFIG_MPC8555CDS)	+= cds_pci_ft.o
+obj-$(CONFIG_TARGET_MPC8555CDS)	+= cds_pci_ft.o
 
 obj-$(CONFIG_TARGET_MPC8536DS)	+= ics307_clk.o
 obj-$(CONFIG_MPC8572DS)	+= ics307_clk.o