Input: ads7846 - be more compatible with the hwmon framework

 - Hook up to hwmon
     * show sensor attributes only if hwmon is present
     * ... and the board's reference voltage is known
     * otherwise be just a touchscreen
 - Report voltages per hwmon convention
     * measure in millivolts
     * voltages are named in[0-8]_input (ugh)
     * for 7846 chips, properly range-adjust vBATT/in1_input

Battery measurements help during recharge monitoring.  On OSK/Mistral,
the measured voltage agreed with a multimeter to several decimal places.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/Kconfig

@@ -12,13 +12,18 @@ menuconfig INPUT_TOUCHSCREEN
 if INPUT_TOUCHSCREEN
 
 config TOUCHSCREEN_ADS7846
-	tristate "ADS 7846 based touchscreens"
+	tristate "ADS 7846/7843 based touchscreens"
 	depends on SPI_MASTER
+	depends on HWMON = n || HWMON
 	help
 	  Say Y here if you have a touchscreen interface using the
-	  ADS7846 controller, and your board-specific initialization
+	  ADS7846 or ADS7843 controller, and your board-specific setup
 	  code includes that in its table of SPI devices.
 
+	  If HWMON is selected, and the driver is told the reference voltage
+	  on your board, you will also get hwmon interfaces for the voltage
+	  (and on ads7846, temperature) sensors of this chip.
+
 	  If unsure, say N (but it's safe to say "Y").
 
 	  To compile this driver as a module, choose M here: the