ACPI: ibm-acpi: fix and extend fan enable

This patch fix fan enable to attempt to do the right thing and not slow
down the fan if it is forced to the maximum speed.  It also extends fan
enable to work on older thinkpads.

ABI changes:
	1.  Support enable/disable for all level-based write access modes

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