NTB: ntb_hw_amd: set peer limit register

As per amd ntb spec it says that peer limit register
must be programmed

Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com>
Acked-by: Allen Hubbe <allenbh@gmail.com>
Acked-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>