broadcom/qpu_instr: wait is not a read or write vpm instruction

For several schedule restrictions, we are checking if the instruction is using the vpm. So far it was implemented as being a read or a write of the vpm. But VPM wait (vpmwt) is not a read or a write (it is a wait until all pending writes finishes). This is relevant to implement peripheral accesses restrictions, as for some cases where vpm read|writes are allowed, vpmwt is not.

Fixes: dEQP-VK.binding_model.descriptorset_random.sets8.constant.ubolimitlow.sbolimitlow.sampledimglow.outimgtexlow.noiub.nouab.vert.noia.0

On the sim, as it was raising an assert for wrong peripheral access.