platform/x86: Add LG Gram laptop special features driver

A driver for LG Gram laptop supporting features not available through the
standard interfaces:

- Support for the 5 Fn keys that generate ACPI or WMI events.

- Two software controlled LEDs: keyboard backlight (also controlled by
  hardware) and touchpad LED.

- Extra features: reader mode, Fn lock, cooling mode, USB charge mode, and
  maximal battery charging level.

Signed-off-by: Matan Ziv-Av <matan@svgalib.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Documentation/ABI/testing/sysfs-platform-lg-laptop

@@ -0,0 +1,35 @@
+What:		/sys/devices/platform/lg-laptop/reader_mode
+Date:		October 2018
+KernelVersion:	4.20
+Contact:	"Matan Ziv-Av <matan@svgalib.org>
+Description:
+        Control reader mode. 1 means on, 0 means off.
+
+What:		/sys/devices/platform/lg-laptop/fn_lock
+Date:		October 2018
+KernelVersion:	4.20
+Contact:	"Matan Ziv-Av <matan@svgalib.org>
+Description:
+        Control FN lock mode. 1 means on, 0 means off.
+
+What:		/sys/devices/platform/lg-laptop/battery_care_limit
+Date:		October 2018
+KernelVersion:	4.20
+Contact:	"Matan Ziv-Av <matan@svgalib.org>
+Description:
+        Maximal battery charge level. Accepted values are 80 or 100.
+
+What:		/sys/devices/platform/lg-laptop/fan_mode
+Date:		October 2018
+KernelVersion:	4.20
+Contact:	"Matan Ziv-Av <matan@svgalib.org>
+Description:
+        Control fan mode. 1 for performance mode, 0 for silent mode.
+
+What:		/sys/devices/platform/lg-laptop/usb_charge
+Date:		October 2018
+KernelVersion:	4.20
+Contact:	"Matan Ziv-Av <matan@svgalib.org>
+Description:
+        Control USB port charging when device is turned off.
+        1 means on, 0 means off.