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/speed.c b/arch/powerpc/cpu/mpc85xx/speed.c
index e4feb3f..7f10ed0 100644
--- a/arch/powerpc/cpu/mpc85xx/speed.c
+++ b/arch/powerpc/cpu/mpc85xx/speed.c
@@ -130,7 +130,7 @@
 	 * it uses 6.
 	 * T2080 rev 1.1 and later also use half mem_pll comparing with rev 1.0
 	 */
-#if defined(CONFIG_PPC_T4240) || defined(CONFIG_ARCH_T4160) || \
+#if defined(CONFIG_ARCH_T4240) || defined(CONFIG_ARCH_T4160) || \
 	defined(CONFIG_PPC_T4080) || defined(CONFIG_ARCH_T2080) || \
 	defined(CONFIG_ARCH_T2081)
 	svr = get_svr();