pinctrl: at91-pio4: Add configuration to userspace

pinctrl: at91-pio4: Add configuration to userspace

Adding support for line bias flags that have been implented in gpio API.
There are functions in the gpiod library that can control line bias from
userspace this adds that functionality to this driver.

Adding .pin_config_set allows the driver's pin configuration to be
accessed from userspace. The general idea for this as been taken from
stm32, intel, and rockchip drivers that have userspace access for bias
flags.

Signed-off-by: Ryan Wanner <Ryan.Wanner@microchip.com>
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sama5d27 som1 ek
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20221007151647.98222-2-Ryan.Wanner@microchip.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>