powerpc: MPC8548: Move CONFIG_MPC8548 to Kconfig option

Replace CONFIG_MPC8548 with ARCH_MPC8548 in Kconfig.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Makefile b/arch/powerpc/cpu/mpc85xx/Makefile
index f4c4fe2..1383454 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -68,7 +68,7 @@
 obj-$(CONFIG_PPC_C29X)	+= c29x_serdes.o
 obj-$(CONFIG_MPC8536) += mpc8536_serdes.o
 obj-$(CONFIG_MPC8544) += mpc8544_serdes.o
-obj-$(CONFIG_MPC8548) += mpc8548_serdes.o
+obj-$(CONFIG_ARCH_MPC8548) += mpc8548_serdes.o
 obj-$(CONFIG_MPC8568) += mpc8568_serdes.o
 obj-$(CONFIG_MPC8569) += mpc8569_serdes.o
 obj-$(CONFIG_MPC8572) += mpc8572_serdes.o