powerpc: MPC8536: Move CONFIG_MPC8536 to Kconfig option

Replace CONFIG_MPC8536 with ARCH_MPC8536 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 640c846..682d4e7 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -56,6 +56,7 @@
 
 config TARGET_MPC8536DS
 	bool "Support MPC8536DS"
+	select ARCH_MPC8536
 
 config TARGET_MPC8540ADS
 	bool "Support MPC8540ADS"
@@ -189,6 +190,9 @@
 config ARCH_C29X
 	bool
 
+config ARCH_MPC8536
+	bool
+
 config ARCH_MPC8544
 	bool
 
diff --git a/arch/powerpc/cpu/mpc85xx/Makefile b/arch/powerpc/cpu/mpc85xx/Makefile
index bfff58e..4733bfd 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -66,7 +66,7 @@
 
 # SoC specific SERDES support
 obj-$(CONFIG_ARCH_C29X)	+= c29x_serdes.o
-obj-$(CONFIG_MPC8536) += mpc8536_serdes.o
+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