gallivm: don't use AoS path if min/mag filter are different with multiple lods

gallivm: don't use AoS path if min/mag filter are different with multiple lods

Instead of enhancing the AoS path so it can deal with it, just use SoA. Fixing
AoS path wouldn't be all that difficult (use all the same logic as SoA) but
considered not worth it for now.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>