IB/core: Add reserved values to enums for low-level driver use

Continue the approach taken by commit d2b57063 ("IB/core: Reserve
bits in enum ib_qp_create_flags for low-level driver use") and add
reserved entries to the ib_qp_type and ib_wr_opcode enums.  Low-level
drivers can then define macros to use these reserved values, giving
proper names to the macros for readability.  Also add a range of
reserved flags to enum ib_send_flags.

The mlx5 IB driver uses the new additions.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <roland@purestorage.com>