ACPI: thinkpad-acpi: add infrastructure for the sysfs device attributes

Add infrastructure to deal with sysfs attributes and grouping, and helpers
for common sysfs parsing.  Switch driver attributes to use them.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>