powerpc: T4160QDS: Separate from T4240QDS in Kconfig

Use TARGET_T4160QDS to simplify Kconfig options.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/T4160QDS_defconfig b/configs/T4160QDS_defconfig
index 109d610..6a169c5 100644
--- a/configs/T4160QDS_defconfig
+++ b/configs/T4160QDS_defconfig
@@ -1,6 +1,6 @@
 CONFIG_PPC=y
 CONFIG_MPC85xx=y
-CONFIG_TARGET_T4240QDS=y
+CONFIG_TARGET_T4160QDS=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y