powerpc: T2080RDB: Rename from T208XRDB in Kconfig

T208XRDB only has one target T2080RDB. Use TARGET_T2080RDB in Kconfig
and clean up existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/T2080RDB_SECURE_BOOT_defconfig b/configs/T2080RDB_SECURE_BOOT_defconfig
index 0818d9c..e5323c4 100644
--- a/configs/T2080RDB_SECURE_BOOT_defconfig
+++ b/configs/T2080RDB_SECURE_BOOT_defconfig
@@ -1,6 +1,6 @@
 CONFIG_PPC=y
 CONFIG_MPC85xx=y
-CONFIG_TARGET_T208XRDB=y
+CONFIG_TARGET_T2080RDB=y
 # CONFIG_SYS_MALLOC_F is not set
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y