spi: atmel: adopt pinctrl support

Amend the spi atmel pin controller to optionally take a pin control
handle and set the state of the pins to:

- "default" on boot, resume and before performing an spitransfer
- "sleep" on suspend()

This should make it possible to optimize energy usage for the pins
both for the suspend/resume cycle

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>