powerpc: T1042D4RDB: Separate from T1042RDB in Kconfig

Use TARGET_T1042D4RDB in Kconfig to simplify config options.
Remove macro CONFIG_T1042D4RDB.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/T1042D4RDB_SECURE_BOOT_defconfig b/configs/T1042D4RDB_SECURE_BOOT_defconfig
index 6382e69..126695d 100644
--- a/configs/T1042D4RDB_SECURE_BOOT_defconfig
+++ b/configs/T1042D4RDB_SECURE_BOOT_defconfig
@@ -1,13 +1,13 @@
 CONFIG_PPC=y
 CONFIG_VIDEO=y
 CONFIG_MPC85xx=y
-CONFIG_TARGET_T1042RDB=y
+CONFIG_TARGET_T1042D4RDB=y
 # CONFIG_SYS_MALLOC_F is not set
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
-CONFIG_SYS_EXTRA_OPTIONS="T1042D4RDB,T104XD4RDB,SYS_FSL_DDR4,SECURE_BOOT"
+CONFIG_SYS_EXTRA_OPTIONS="T104XD4RDB,SYS_FSL_DDR4,SECURE_BOOT"
 CONFIG_BOOTDELAY=10
 CONFIG_SILENT_CONSOLE=y
 # CONFIG_CONSOLE_MUX is not set