NTB: switchtec_ntb: Initialize hardware for memory windows

Add the code to initialize the memory windows in the hardware.
This includes setting up the requester ID table, and figuring out
which BAR corresponds to which memory window. (Seeing the switch
can be configured with any number of BARs.)

Also, seeing the device doesn't have hardware for scratchpads or
determining the link status, we create a shared memory window that has
these features. A magic number with a version component will be used
to determine if the other side's driver is actually up.

The shared memory window also informs the other side of the
size and count of the local memory windows.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Stephen Bates <sbates@raithlin.com>
Reviewed-by: Kurt Schwemmer <kurt.schwemmer@microsemi.com>
Acked-by: Allen Hubbe <Allen.Hubbe@dell.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>