mlx4_core: Rename MPT-related functions to have mpt_ prefix

The MPT - Memory Protection Table - is used by both memory windows and
memory regions.  Hence, all MPT references are relevant for both types
of memory objects.  Rename the relevant functions to start with mpt_
instead of the current mr_ prefix.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Shani Michaeli <shanim@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>