IB/ipath: Remove incompletely implemented ipath_runtime flags and code

The IPATH_RUNTIME_PBC_REWRITE and the IPATH_RUNTIME_LOOSE_DMA_ALIGN
flags were not ever implemented correctly and did not turn out to be
necessary.  Remove the last vestiges of these flags but mark the spot
with a comment to remind us to not reuse these flags in the interest
of binary compatibility.  The INFINIPATH_XGXS_SUPPRESS_ARMLAUNCH_ERR
bit was also not found to be useful, so it was dropped in the cleanup
as well.

Signed-off-by: John Gregor <john.gregor@qlogic.com>
Signed-off-by: Arthur Jones <arthur.jones@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>