powerpc: T4240: Remove macro CONFIG_PPC_T4240

Use CONFIG_ARCH_T4240 from Kconfig instead.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/t4240_serdes.c b/arch/powerpc/cpu/mpc85xx/t4240_serdes.c
index 4b73e76..1a5bcb1 100644
--- a/arch/powerpc/cpu/mpc85xx/t4240_serdes.c
+++ b/arch/powerpc/cpu/mpc85xx/t4240_serdes.c
@@ -15,7 +15,7 @@
 	u8 lanes[SRDS_MAX_LANES];
 };
 
-#ifdef CONFIG_PPC_T4240
+#ifdef CONFIG_ARCH_T4240
 static const struct serdes_config serdes1_cfg_tbl[] = {
 	/* SerDes 1 */
 	{1, {XAUI_FM1_MAC9, XAUI_FM1_MAC9,