staging: typec: fusb302: Get max snk mv/ma/mw from device-properties

This is board specific info so it should come from board config, such
as devicetree.

I've chosen to prefix these with "fcs," treating them as fusb302 driver
specific for now. We may want to revisit this and replace these with
properties which are part of a (to be written) generic type-c controller
devicetree binding.

Since this commit adds new dt-properties it also adds devicetree-bindings
documentation (which so far was absent for the fusb302 driver).

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: devicetree@vger.kernel.org
Cc: "Yueyao (Nathan) Zhu" <yueyao@google.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>