powerpc: T1040D4RDB: Separate from T1040RDB in Kconfig

Use TARGET_T1040D4RDB in Kconfig to simplify config macros. Replace
CONFIG_T1040D4RDB with TARGET_T1040D4RDB and clean up existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index bad4af6..5958536 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -218,6 +218,12 @@
 	select SUPPORT_SPL
 	select PHYS_64BIT
 
+config TARGET_T1040D4RDB
+	bool "Support T1040D4RDB"
+	select ARCH_T1040
+	select SUPPORT_SPL
+	select PHYS_64BIT
+
 config TARGET_T1042RDB
 	bool "Support T1042RDB"
 	select SUPPORT_SPL