platform/x86: Add new intel_atomisp2_led driver

platform/x86: Add new intel_atomisp2_led driver

Many Bay Trail and Cherry Trail devices come with a camera attached to
Intel's Image Signal Processor. Linux currently does not have a driver for
these, so they do not work as a camera.

Some of these camera's have a status LED which is controlled through a GPIO
in some cases, e.g. on the Asus T100TA and Asus T200TA, there is a firmware
issue where the LED gets turned on at boot.

This commit adds a Linux LED driver for the camera LED on these devices.
This driver will turn the LED off at boot and also allows controlling the
LED (so the user can repurpose it) through the sysfs LED interface.

Which GPIO is attached to the LED is usually not described in the ACPI
tables, so this driver contains per-system info about the GPIO inside the
driver. This means that this driver only works on systems the driver knows
about.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>