ntb: Adding Skylake Xeon NTB support

The Skylake Xeon NTB hardware has made some changes to the register name,
offset, and the way doorbells work. Adding driver support for the new
hardware.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Allen Hubbe <Allen.Hubbe@dell.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>