spi: at91-usart: replacing legacy gpio interface for gpiod

Removing dependency of linux/of_gpio.h and replacing it for
linux/gpio/consumer.h

Signed-off-by: Maíra Canal <maira.canal@usp.br>
Link: https://lore.kernel.org/r/YW8I5Emdc3t0cqhz@fedora
Signed-off-by: Mark Brown <broonie@kernel.org>