ACPI: thinkpad-acpi: add compatibility MODULE_ALIAS entry

Add a ibm_acpi module alias for userpace, so that modprobe ibm_acpi will
still load the correct driver.  This alias can be removed in the future,
probably two years from now if nothing warrants removing it sooner.

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