powerpc: P1024RDB: Separate from P1_P2_RDB_PC in Kconfig

Use TARGET_P1024RDB instead of sharing with TARGET_P1_P2_RDB_PC to
simplify Kconfig and macros.

Remove macro CONFIG_P1024RDB.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/include/configs/p1_p2_rdb_pc.h b/include/configs/p1_p2_rdb_pc.h
index f68feb3..eb88576 100644
--- a/include/configs/p1_p2_rdb_pc.h
+++ b/include/configs/p1_p2_rdb_pc.h
@@ -118,7 +118,7 @@
 #endif
 #endif
 
-#if defined(CONFIG_P1024RDB)
+#if defined(CONFIG_TARGET_P1024RDB)
 #define CONFIG_BOARDNAME "P1024RDB"
 #define CONFIG_NAND_FSL_ELBC
 #define CONFIG_P1024