staging/rdma/hfi1: Use parallel workqueue for SDMA engines

The workqueue is currently single threaded per port which for a small number of
SDMA engines is ok.

For hfi1, the there are up to 16 SDMA engines that can be fed descriptors in
parallel.

Use alloc_workqueue with a workqueue limit of the number of sdma engines and
with WQ_CPU_INTENSIVE and WQ_HIGHPRI specified.

Then change send to use the new scheduler which no longer needs to get the
s_lock

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>