thinkpad-acpi: clean up ACPI handles handling

1. Remove <handle>_path, as its only user was already removed in
   a previous commit

2. Move all handle initialization, as well as <handle>_parent and
   <handle>_paths to __init.* sections.  This reduces the driver's
   runtime footprint nicely.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>