dt-bindings: gnss: add sirfstar binding

Add binding for SiRFstar-based GNSS receivers.

Note that while four compatible-strings are initially added representing
devices which differ in which I/O interfaces they support, they
otherwise essentially share the same feature set.

Pin and supply names vary slightly, as do some recommended timings.

Note that the wakeup gpio is not intended to be used as a wakeup source,
but rather to detect the current power state of the device (active or
hibernate).

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>