drivers: atmel_piobu: add driver

Add piobu driver which handle secumod GPIOs. This driver also handle
tampering interrupts on GPIOs which are configured as input with the
device-tree. For instance,

drivers: atmel_piobu: add driver

Add piobu driver which handle secumod GPIOs. This driver also handle
tampering interrupts on GPIOs which are configured as input with the
device-tree. For instance, the following device-tree excerpt allows to
set an input as an intrusion detection pin:

gpios = <0 PIOBU_PIN_INPUT(1, 1, PIOBU_PIN_PULL_DOWN,
PIOBU_PIN_DEF_LEVEL_LOW, PIOBU_PIN_WAKEUP_ENABLE)>;

In case of a tamper event, the source of the tampering will be
displayed.

Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Clément Léger <clement.leger@bootlin.com>

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