RDMA/qedr: properly check atomic capabilities

After checking the path upwards towards root complex, actualy check
root complex atomic_req capability, and not our own NIC.
Verify that the PCIe device control register's atomic egress block
is cleared in the path.
Verify that the PCIe version is at least 2.

Signed-off-by: Ram Amrani <Ram.Amrani@cavium.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>