dt-bindings: add documentation for banks

Add documentation for at91 pin controller banks.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
1 file changed