model_id fields of wf_smu_sys_all_params should match the model ID
they are supposed to represent (as commented). Fixes windfarm on some
iMac 8,1 models.

Signed-off-by: Michal Ostrowski <mostrows at watson ibm com>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>