ARM: dts: sun6i: sina31s: Enable USB OTG controller in peripheral mode

While the SinA31s does have a proper 5-pin mini USB OTG port, the ID
pin does not seem to work. The pin used in the schematics is always low,
regardless of the attached OTG cable or SoC internal pin bias settings.

The v1.5 board is missing bias resistors shown in the schematics for
earlier revisions, and the connections of the remaining one does not
match the schematics either.

In addition, VBUS for this port is disconnected from the board's 5V
power rail. The board features a pad to solder jumper pins to connect
VBUS to 5V manually.

Given the above and the fact that the board has 5 more USB host ports,
it makes more sense to have the OTG port work in peripheral mode.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>