devlink: add a driver-specific file for the qed driver

The qed driver recently added devlink support with a single devlink
parameter. Add a driver-specific file to document the devlink features
that the qed driver supports.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Ariel Elior <aelior@marvell.com>
Cc: GR-everest-linux-l2@marvell.com
Signed-off-by: David S. Miller <davem@davemloft.net>