iio:proximity:sx9310: Extract common Semtech sensor logic

Before adding new Semtech sensors, move common logic to all Semtech SAR
sensor in its own file:
- interface with IIO subsystem,
- interrupt management,
- channel access conrol,
- event processing.

The change adds a bidirectional interface between sx93xx and sx_common.

The change is quite mechanical, as the impacted functions are moved
and renamed.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20220101203817.290512-3-gwendal@chromium.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/proximity/Kconfig

@@ -112,11 +112,17 @@ config SRF04
 	  To compile this driver as a module, choose M here: the
 	  module will be called srf04.
 
+config SX_COMMON
+	tristate
+	help
+	  Common Semtech proximity sensor code.
+
 config SX9310
 	tristate "SX9310/SX9311 Semtech proximity sensor"
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 	select REGMAP_I2C
+	select SX_COMMON
 	depends on I2C
 	help
 	  Say Y here to build a driver for Semtech's SX9310/SX9311 capacitive

drivers/iio/proximity/Makefile

@@ -14,6 +14,7 @@ obj-$(CONFIG_RFD77402)		+= rfd77402.o
 obj-$(CONFIG_SRF04)		+= srf04.o
 obj-$(CONFIG_SRF08)		+= srf08.o
 obj-$(CONFIG_SX9310)		+= sx9310.o
+obj-$(CONFIG_SX_COMMON) 	+= sx_common.o
 obj-$(CONFIG_SX9500)		+= sx9500.o
 obj-$(CONFIG_VCNL3020)		+= vcnl3020.o
 obj-$(CONFIG_VL53L0X_I2C)	+= vl53l0x-i2c.o