powerpc: Enable device tree support for P1020RDB

Add device tree for P1020RDB boards and enable CONFIG_OF_CONTROL
so that device tree can be compiled.
Update board README for device tree usage.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
diff --git a/configs/P1020RDB-PC_defconfig b/configs/P1020RDB-PC_defconfig
index dec97c4..ea57e52 100644
--- a/configs/P1020RDB-PC_defconfig
+++ b/configs/P1020RDB-PC_defconfig
@@ -3,6 +3,7 @@
 CONFIG_MPC85xx=y
 # CONFIG_CMD_ERRATA is not set
 CONFIG_TARGET_P1020RDB_PC=y
+CONFIG_MPC85XX_HAVE_RESET_VECTOR=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
@@ -25,6 +26,8 @@
 # CONFIG_CMD_HASH is not set
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
+CONFIG_OF_CONTROL=y
+CONFIG_DEFAULT_DEVICE_TREE="p1020rdb-pc"
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_FSL_ESDHC=y
 CONFIG_MTD_NOR_FLASH=y
@@ -45,4 +48,3 @@
 CONFIG_FSL_ESPI=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
-CONFIG_OF_LIBFDT=y