powerpc: Enable device tree support for T1042D4RDB

Add device tree for T1042D4RDB board 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/arch/powerpc/dts/Makefile b/arch/powerpc/dts/Makefile
index b7acba5..f0d49aa 100644
--- a/arch/powerpc/dts/Makefile
+++ b/arch/powerpc/dts/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0+
 
 dtb-$(CONFIG_TARGET_T1024RDB) += t1024rdb.dtb
+dtb-$(CONFIG_TARGET_T1042D4RDB) += t1042d4rdb.dtb
 dtb-$(CONFIG_TARGET_T2080QDS) += t2080qds.dtb
 dtb-$(CONFIG_TARGET_T2080RDB) += t2080rdb.dtb
 dtb-$(CONFIG_TARGET_T4240RDB) += t4240rdb.dtb