ntb_hw_switchtec: AND with the part_map for a valid tpart_vec

Some firmware versions return 1 in the target partition vector for
undefined partitions. AND with the part_map to give a valid tpart_vec.

Signed-off-by: Jeremy Pallotta <jmpallotta@gmail.com>
Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>