powerpc: P1020RDB-PC: Separate from P1_P2_RDB_PC in Kconfig

Use TARGET_P1020RDB_PC instead of sharing with TARGET_P1_P2_RDB_PC
to simplify Kconfig and config macros.

Remove macro CONFIG_P1020RDB_PC.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/freescale/p1_p2_rdb_pc/Kconfig b/board/freescale/p1_p2_rdb_pc/Kconfig
index 2c45560..6fa6859 100644
--- a/board/freescale/p1_p2_rdb_pc/Kconfig
+++ b/board/freescale/p1_p2_rdb_pc/Kconfig
@@ -1,5 +1,6 @@
-if TARGET_P1_P2_RDB_PC || \
-	TARGET_P1020MBG
+if TARGET_P1_P2_RDB_PC		|| \
+	TARGET_P1020MBG		|| \
+	TARGET_P1020RDB_PC
 
 config SYS_BOARD
 	default "p1_p2_rdb_pc"