ARM: dts: Add devicetree for Samsung GT-S7710

The Samsung GT-S7710 also known as XCover 2 or Skomer is a
Ux500-based mobile phone. In the source code release from
Samsung's open source site it is referred to as "Skomer".

Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20200307193627.4092-1-linus.walleij@linaro.org


[Typographic fixups when applying]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>