powerpc: T208XQDS: Split as T2080QDS and T2081QDS

Use two separated targets in Kconfig to simplify configurations.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/T2081QDS_defconfig b/configs/T2081QDS_defconfig
index 07ff6b6..e35c003 100644
--- a/configs/T2081QDS_defconfig
+++ b/configs/T2081QDS_defconfig
@@ -1,6 +1,6 @@
 CONFIG_PPC=y
 CONFIG_MPC85xx=y
-CONFIG_TARGET_T208XQDS=y
+CONFIG_TARGET_T2081QDS=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y