dt-bindings: i2c: at91: document optional bus recovery properties

The at91 I2C controller can support bus recovery by re-assigning SCL
and SDA to gpios. Add the optional pinctrl and gpio properties to do
so.

Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
[codrin.ciubotariu@microchip.com: rebased]
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>