thinkpad-acpi: expose module parameters

Export the normal (non-command) module paramenters as mode 0444, so
that they will show up in sysfs.

These parameters must not be changed at runtime as a rule, with very
few exceptions.

Reported-by: Ferenc Wagner <wferi@niif.hu>
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>