powerpc: C29X: Move CONFIG_PPC_C29X to Kconfig option

Replace CONFIG_PPC_C29X with ARCH_C29X 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 e545112..bfff58e 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -65,7 +65,7 @@
 obj-$(CONFIG_SYS_FSL_QORIQ_CHASSIS2) += fsl_corenet2_serdes.o
 
 # SoC specific SERDES support
-obj-$(CONFIG_PPC_C29X)	+= c29x_serdes.o
+obj-$(CONFIG_ARCH_C29X)	+= c29x_serdes.o
 obj-$(CONFIG_MPC8536) += mpc8536_serdes.o
 obj-$(CONFIG_ARCH_MPC8544) += mpc8544_serdes.o
 obj-$(CONFIG_ARCH_MPC8548) += mpc8548_serdes.o