Version dk01.1-c1 didn't have compatible specified, which was
causing dt-schema validation warnings.

Remove duplicated and useless board compatible from dtsi between board and device.
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211009193102.76852-2-david@ixit.cz