powerpc: MPC8572: Remove macro CONFIG_MPC8572

Replace CONFIG_MPC8572 with ARCH_MPC8572 in Kconfig and clean up existing
macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Makefile b/arch/powerpc/cpu/mpc85xx/Makefile
index 9df1434..e3f7dc8 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -71,7 +71,7 @@
 obj-$(CONFIG_ARCH_MPC8548) += mpc8548_serdes.o
 obj-$(CONFIG_ARCH_MPC8568) += mpc8568_serdes.o
 obj-$(CONFIG_ARCH_MPC8569) += mpc8569_serdes.o
-obj-$(CONFIG_MPC8572) += mpc8572_serdes.o
+obj-$(CONFIG_ARCH_MPC8572) += mpc8572_serdes.o
 obj-$(CONFIG_P1010)	+= p1010_serdes.o
 obj-$(CONFIG_P1011)	+= p1021_serdes.o
 obj-$(CONFIG_P1012)	+= p1021_serdes.o