powerpc: MPC8568: Remove macro CONFIG_MPC8568

Replace CONFIG_MPC8568 with ARCH_MPC8568 in Kconfig and clean up existing
macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 98f98af..9545793 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -84,6 +84,7 @@
 
 config TARGET_MPC8568MDS
 	bool "Support MPC8568MDS"
+	select ARCH_MPC8568
 
 config TARGET_MPC8569MDS
 	bool "Support MPC8569MDS"
@@ -215,6 +216,9 @@
 config ARCH_MPC8560
 	bool
 
+config ARCH_MPC8568
+	bool
+
 source "board/freescale/b4860qds/Kconfig"
 source "board/freescale/bsc9131rdb/Kconfig"
 source "board/freescale/bsc9132qds/Kconfig"
diff --git a/arch/powerpc/cpu/mpc85xx/Makefile b/arch/powerpc/cpu/mpc85xx/Makefile
index 4733bfd..390eede 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -69,7 +69,7 @@
 obj-$(CONFIG_ARCH_MPC8536) += mpc8536_serdes.o
 obj-$(CONFIG_ARCH_MPC8544) += mpc8544_serdes.o
 obj-$(CONFIG_ARCH_MPC8548) += mpc8548_serdes.o
-obj-$(CONFIG_MPC8568) += mpc8568_serdes.o
+obj-$(CONFIG_ARCH_MPC8568) += mpc8568_serdes.o
 obj-$(CONFIG_MPC8569) += mpc8569_serdes.o
 obj-$(CONFIG_MPC8572) += mpc8572_serdes.o
 obj-$(CONFIG_P1010)	+= p1010_serdes.o