ARM64: dts: rockchip: Tiny comment cleanups for kevin-r0

ARM64: dts: rockchip: Tiny comment cleanups for kevin-r0

I was having a hard time figuring out where to put new things in
kevin-r0.  Add some comments to explain the sort order.

BUG=None
TEST=Build and boot

Change-Id: I9fb8c200f934542ebed984566bab039d4ec3fd13
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chrome-internal-review.googlesource.com/256509
Commit-Ready: Doug Anderson <dianders@google.com>
Tested-by: Doug Anderson <dianders@google.com>
Reviewed-by: Brian Norris <briannorris@google.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>