platform/x86: thinkpad_acpi: Convert platform driver to use dev_groups

Platform drivers have the option of having the platform core create and
remove any needed sysfs attribute files. So take advantage of that and
refactor the attributes management to avoid to register them "by hand".

Also, due to some attributes are optionals, refactor the code and move
the logic inside the "is_visible" callbacks of the attribute_group
structures.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Len Baker <len.baker@gmx.com>