qedr: Add wrapping generic structure for qpidr and adjust idr routines.

Today, we are using idr mechanism for QP's only.
This patch prepares the qedr_idr stuctures and the idr routines for
both QP's and SRQ's.

Signed-off-by: Yuval Bason <yuval.bason@cavium.com>
Signed-off-by: Michal Kalderon <michal.kalderon@cavium.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>