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_NAND_defconfig b/configs/T2080RDB_NAND_defconfig
index 5e17f3b..cf402ff 100644
--- a/configs/T2080RDB_NAND_defconfig
+++ b/configs/T2080RDB_NAND_defconfig
@@ -7,7 +7,7 @@
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_DRIVERS_MISC_SUPPORT=y
 CONFIG_MPC85xx=y
-CONFIG_TARGET_T208XRDB=y
+CONFIG_TARGET_T2080RDB=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y