iio: adxl372: Refactor the driver

This patch restructures the existing adxl372 driver by adding a module for
SPI and a header file, while the baseline module deals with the chip-logic.

This is a necessary step, as this driver should support in the future
a similar device which differs only in the type of interface used (I2C
instead of SPI).

Signed-off-by: Stefan Popa <stefan.popa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
index eae23d6..bed5da8 100644
--- a/drivers/iio/accel/Kconfig
+++ b/drivers/iio/accel/Kconfig
@@ -61,15 +61,20 @@
 	  for the core module.
 
 config ADXL372
-	tristate "Analog Devices ADXL372 3-Axis Accelerometer Driver"
-	depends on SPI
+	tristate
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
+
+config ADXL372_SPI
+	tristate "Analog Devices ADXL372 3-Axis Accelerometer SPI Driver"
+	depends on SPI
+	select ADXL372
+	select REGMAP_SPI
 	help
 	  Say yes here to add support for the Analog Devices ADXL372 triaxial
 	  acceleration sensor.
 	  To compile this driver as a module, choose M here: the
-	  module will be called adxl372.
+	  module will be called adxl372_spi.
 
 config BMA180
 	tristate "Bosch BMA180/BMA250 3-Axis Accelerometer Driver"