iop-adma: P+Q self test

Even though the intent is to extend dmatest with P+Q tests there is
still value in having an always-on sanity check to prevent an
unintentionally broken driver from registering.

This depends on raid6_pq.ko for verification, the side effect being that
PQ capable channels will fail to register when raid6 is disabled.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>