[IB] uverbs: Add ABI structures for more commands

Add kernel/user ABI structures for marshalling poll CQ, request CQ
notification, post send, post receive, post SRQ receive, create AH and
destroy AH commands.  These commands allow us to support userspace
verbs for devices that can't perform these operations directly from
userspace (eg the PathScale HCA).

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