IB/{hfi1, qib, rdmavt}: Move logic to allocate receive WQE into rdmavt

IB/{hfi1, qib, rdmavt}: Move logic to allocate receive WQE into rdmavt

Moving receive-side WQE allocation logic into rdmavt will allow
further code reuse between qib and hfi1 drivers.

Reviewed-by: Mike Marciniszyn <[email protected]>
Reviewed-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Brian Welty <[email protected]>
Signed-off-by: Harish Chegondi <[email protected]>
Signed-off-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>