powerpc: T104XRDB: Split to T1040RDB and T1042RDB in Kconfig

Split ARCH_T104XRDB as ARCH_T1040RDB and ARCH_T1042RDB in Kconfig to
simplify config options.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/freescale/t104xrdb/Kconfig b/board/freescale/t104xrdb/Kconfig
index f28728d..5b6095b 100644
--- a/board/freescale/t104xrdb/Kconfig
+++ b/board/freescale/t104xrdb/Kconfig
@@ -1,4 +1,4 @@
-if TARGET_T104XRDB
+if TARGET_T1040RDB || TARGET_T1042RDB
 
 config SYS_BOARD
 	default "t104xrdb"