powerpc: P1025RDB: Separate from P1_P2_RDB_PC in Kconfig

Use TARGET_P1025RDB instead of sharing with P1_P2_RDB_PC to
simplify Kconfig and config macros.

Remove macro CONFIG_P1025RDB.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/freescale/p1_p2_rdb_pc/ddr.c b/board/freescale/p1_p2_rdb_pc/ddr.c
index 446935e..44ab123 100644
--- a/board/freescale/p1_p2_rdb_pc/ddr.c
+++ b/board/freescale/p1_p2_rdb_pc/ddr.c
@@ -147,7 +147,7 @@
 	.tfaw_ps = 37500,
 };
 #elif	defined(CONFIG_TARGET_P1024RDB) || \
-	defined(CONFIG_P1025RDB)
+	defined(CONFIG_TARGET_P1025RDB)
 /*
  * Samsung K4B2G0846C-HCH9
  * The following timing are for "downshift"