test: fdtdec: test fdtdec_set_carveout()

Add a new test for fdtdec_set_carveout().

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Drop blank line at EFO:
Signed-off-by: Simon Glass <sjg@chromium.org>