Partially revert "[SchedModels][CortexA55] Add ASIMD integer instructions"

The Cortex-A55 scheduling model is used for -mcpu=generic, meaning it
can have a wider effect than just the A55. The changes to the A55
scheduling model seems to have caused performance regressions on
Cortex-A510 device which have latencies closer to the original and
different forwarding paths.

This partially reverts the changes from D117003, at least until we can
do something to improve Cortex-A510. According to my results, this
improves the A510 results without altering the A55 very much.