Make sure RQ allocation is always valid

Make sure RQ allocation is always valid

QPs attached to an SRQ must never have their own RQ, and QPs not
attached to SRQs must have an RQ with at least 1 entry.  Enforce all
of this in set_rq_size().

Also simplify how we round up queue sizes.  There's no need to pass the
context into align_queue_size(), since that parameter is completely
unused, and we don't really need two functions for rounding up to the
next power of two.

Signed-off-by: Roland Dreier <rolandd@cisco.com>