Enabling OF selftest to run without machine's devicetree

If there is no devicetree present, this patch adds the selftest
data as a live devicetree. It also removes the same after the
testcase execution is complete.

Tested with and without machine's devicetree.

Signed-off-by: Gaurav Minocha <gaurav.minocha.os@gmail.com>
Signed-off-by: Grant Likely <grant.likely@linaro.org>