docs: dt: submitting-patches: Add note about other project usage

docs: dt: submitting-patches: Add note about other project usage

In an attempt to make it more broadly known that other projects are
equal consumers / users of the device tree bindings, add a note to
submitting patches to say that extra care and consideration may need to
be taken when updating existing bindings.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tom Rini <trini@konsulko.com>
Link: https://lore.kernel.org/r/20210910142419.5237-1-trini@konsulko.com
Signed-off-by: Rob Herring <robh@kernel.org>