iio: gyro: st_gyro: Move platform data from header to C file

Platform data is solely used by one file. Don't share it with others.

While at it, drop unneeded anymore __maybe_unused and fix kernel doc
to avoid warning:

  st_gyro_core.c:366: error: Cannot parse struct or union!

by converting to a simple comment. It is described at the declaration.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210414195454.84183-2-andriy.shevchenko@linux.intel.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/gyro/st_gyro.h

@@ -24,14 +24,6 @@
 #define LSM330_GYRO_DEV_NAME		"lsm330_gyro"
 #define LSM9DS0_GYRO_DEV_NAME		"lsm9ds0_gyro"
 
-/**
- * struct st_sensors_platform_data - gyro platform data
- * @drdy_int_pin: DRDY on gyros is available only on INT2 pin.
- */
-static __maybe_unused const struct st_sensors_platform_data gyro_pdata = {
-	.drdy_int_pin = 2,
-};
-
 const struct st_sensor_settings *st_gyro_get_settings(const char *name);
 int st_gyro_common_probe(struct iio_dev *indio_dev);
 void st_gyro_common_remove(struct iio_dev *indio_dev);

drivers/iio/gyro/st_gyro_core.c

@@ -357,6 +357,11 @@ static const struct st_sensor_settings st_gyro_sensors_settings[] = {
 	},
 };
 
+/* DRDY on gyros is available only on INT2 pin */
+static const struct st_sensors_platform_data gyro_pdata = {
+	.drdy_int_pin = 2,
+};
+
 static int st_gyro_read_raw(struct iio_dev *indio_dev,
 			struct iio_chan_spec const *ch, int *val,
 							int *val2, long mask)