Implement function to generate internal test DT fragment and switch
the 'fdt get value' test to this instead of depending on the sandbox
DT. Rename clk-test node to test-node node. This FDT fragment will be
reused by other tests. No functional change.
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>