ARM: dts: rockchip: pull up cts lines on rk3288

The flow control lines from a user accessible UART are optional,
the user might not have anything connected to those pins.
In order to prevent random interrupts happening and noise affecting
the cts pin should be pulled up.

Note that the default state for that pin on the rk3288 is pulled up,
so this patch merely restores them.

This is similar to what we're already doing with the RX pin,
so it should be safe. At worst it might be a slightly higher power usage
(through ~50 kohms) when the cts is low.

Suggested-by: Neil Hendin <nhendin@chromium.org>
Signed-off-by: Alexandru M Stan <amstan@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>