arm64: dts: rockchip: add Google Bob

After Kevin, the second chromebook-incarnation of the Gru series is Bob.
This materializes as the Asus Chromebook Flip C101PA, whose formfactor
is quite similar to Minnie from the Veyron series.

Add the devicetree file and binding update for it.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>