dt-bindings: gpio: Convert mrvl-gpio to json-schema

dt-bindings: gpio: Convert mrvl-gpio to json-schema

This converts the mrvl-gpio binding to DT schema format using json-schema.

Various fixes were done during the conversion, such as adding more
properties that are in fact mandatory or extending the examples to
include child nodes with extra GPIO blocks.

The compatible strings are a mess. It is not clear why so many of them
are needed; the driver doesn't really seem to differentiate between the
models. Some of them, like marvell,pxa93x-gpio and marvell,pxa1928-gpio
are not used at all, so it's not known how many interrupts they utilize.
On the other hand, mrvl,pxa-gpio has been seen in the tree, but it
doesn't end up in any actual DTB file.

In any case -- the schema merely copies whatever was in the original
binding document, so it's hopefully no more wrong that the original.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20200616223353.993567-2-lkundrak@v3.sk
Signed-off-by: Rob Herring <robh@kernel.org>