igb: move SDP config initialization to separate function

Allow reuse of SDP config struct initialization by moving it to a
separate function.

Signed-off-by: Ruud Bos <kernel.hbk@gmail.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>