ACPI: Add sysfs ABI documentation

Add initial ABI documentation for ACPI devices' sysfs interfaces.
Contacts information fields are filled with current ACPI maintainer and the
relevant authors are carbon copied.

[rjw: Use my e-mail address that's likely to be valid longer.]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>