iio: adc: ltc2497: split protocol independent part in a separate module

This allows to share most of this driver for the ltc2496 driver added in
the next commit that is an SPI variant of the ltc2497. Initially I named
the generic part ltc249x, but wild card names are frowned upon, so the
generic part is called ltc2497-core even though it's not obvious that
this is then to be reused for the ltc2496 driver.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
new file mode 100644
index 0000000..d0b42dd
--- /dev/null
+++ b/drivers/iio/adc/ltc2497.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#define LTC2497_ENABLE			0xA0
+#define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
+#define LTC2497_CONVERSION_TIME_MS	150ULL
+
+struct ltc2497core_driverdata {
+	struct regulator *ref;
+	ktime_t	time_prev;
+	u8 addr_prev;
+	int (*result_and_measure)(struct ltc2497core_driverdata *ddata,
+				  u8 address, int *val);
+};
+
+int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev);
+void ltc2497core_remove(struct iio_dev *indio_dev);
+
+MODULE_IMPORT_NS(LTC2497);