i2c: of-prober: Add GPIO support to simple helpers

Add GPIO support to the simple helpers for the I2C OF component prober.
Components that the prober intends to probe likely require their
regulator supplies be enabled, and GPIOs be toggled to enable them or
bring them out of reset before they will respond to probe attempts.
Regulator supplies were handled in the previous patch.

The assumption is that the same class of components to be probed are
always connected in the same fashion with the same regulator supply
and GPIO. The names may vary due to binding differences, but the
physical layout does not change.

This supports at most one GPIO pin. The user must specify the GPIO name,
the polarity, and the amount of time to wait after the GPIO is toggled.
Devices with more than one GPIO pin likely require specific power
sequencing beyond what generic code can easily support.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>