platform/oaktrail: ACPI EC Extra driver for Oaktrail

This driver implements an Extra ACPI EC driver for products based on Intel
Oaktrail platform.

This driver does below things:
1. registers itself in the Linux backlight control in
   /sys/class/backlight/intel_oaktrail/

2. registers in the rfkill subsystem here: /sys/class/rfkill/rfkillX/
   for these components: wifi, bluetooth, wwan (3g), gps

Signed-off-by: Yin Kangkai <kangkai.yin@linux.intel.com>

[Extracted from a bigger patch by Yin Kangkai, this version leaves out some
 sysfs bits that probably want to be driver managed, and ACPI i2c enumeration]

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>