mlx4_core: Reduce number of PD bits to 17

When SRIOV is enabled on the chip (at FW burning time),
the HCA uses only 17 bits for the PD. The remaining 7 high-order bits
are ignored.

Change the allocator to return only 17 bits for the PD.  The MSB 7
bits will be used to encode the slave number for consistency
checking later on in the resource tracker.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>