ARM: mstar: Add gpio controller to MStar base dtsi

The GPIO controller is at the same address in all of the
currently known chips so create a node for it in the base
dtsi.

Some extra properties are needed to actually use it so
disable it by default.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201129110803.2461700-5-daniel@0x0f.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>