dt-bindings: net: Add rfkill-gpio binding

Add a device tree binding document for GPIO controlled rfkill switches.
The label and radio-type properties correspond to the name and type
properties used for ACPI, respectively. The shutdown-gpios property
is the same as defined for ACPI.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230102-rfkill-gpio-dt-v2-1-d1b83758c16d@pengutronix.de


Signed-off-by: Johannes Berg <johannes.berg@intel.com>