The sx8654 features a NRST input which may be connected to a GPIO.
Therefore add support for hard-resetting the sx8654 via this NRST.

If the reset-gpio property is provided the sx8654 is resetted via NRST
instead of the soft-reset via I2C.
Signed-off-by: NRichard Leitner <richard.leitner@skidata.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>