IB/ipath: Be more cautious about coming out of freeze mode

We are more careful to be sure that we don't lose information about
changes that occurred while we were in freeze mode, when the chip will
not notify us, and try to avoid false error interrupts while doing
cleanup.  Put all of this logic in a new function ipath_clear_freeze().

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>