iio: resolver: ad2s1210: add reset gpio support

This adds support for the optional reset gpio to the ad2s1210 resolver
driver. If the gpio is present in the device tree, it is toggled during
driver probe before the reset of the device initialization. As per the
devicetree bindings, it is expected for the gpio to configured as active
low.

Suggested-by: Michael Hennerich <Michael.Hennerich@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20231016154311.38547-1-dlechner@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: resolver: ad2s1210: add support for adi,fixed-mode

It is possible to use the AD2S1210 with hardwired mode pins (A0 and A1).
According to the devicetree bindings, in this case the adi,fixed-mode
property will specify which of the 3 possible modes the mode pins are
hardwired for and the gpio-modes property is not allowed.

This adds support for the case where the mode pins are hardwired for
config mode. In this configuration, the position and value must be read
from the config register.

The case of hardwired position or velocity mode is not supported as
there would be no way to configure the device.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20231016135423.16808-1-dlechner@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: resolver: ad2s1210: remove of_match_ptr()

To be consistent with the rest of iio, remove of_match_ptr(). It does
not do anything useful here.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231012-ad2s1210-mainline-v1-2-b2ee31c0e9dd@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: resolver: ad2s1210: remove DRV_NAME macro

The DRV_NAME macro is only used in one place in the ad2s1210 driver and
is not really needed so let's remove it.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231012-ad2s1210-mainline-v1-1-b2ee31c0e9dd@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: resolver: ad2s1210: move out of staging

This moves the ad2s1210 resolver driver out of staging. The driver has
been fixed up and is ready to graduate.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231010-ad2s1210-mainline-v5-4-35a0f6ffa04a@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>