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/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 991127d..83dd1e0 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -274,11 +274,13 @@
 
 config TARGET_T4240QDS
 	bool "Support T4240QDS"
+	select ARCH_T4240
 	select SUPPORT_SPL
 	select PHYS_64BIT
 
 config TARGET_T4240RDB
 	bool "Support T4240RDB"
+	select ARCH_T4240
 	select SUPPORT_SPL
 	select PHYS_64BIT
 
@@ -424,6 +426,9 @@
 config ARCH_T4160
 	bool
 
+config ARCH_T4240
+	bool
+
 source "board/freescale/b4860qds/Kconfig"
 source "board/freescale/bsc9131rdb/Kconfig"
 source "board/freescale/bsc9132qds/Kconfig"