drcachesim offline traces do not handle large cache flush sizes properly

The comment in trace_entry.h explains it pretty well:
```
// On ARM, a flush is requested via a SYS_cacheflush system call,
// and the flush size could be larger than USHRT_MAX.
// If the size is smaller than USHRT_MAX, we use one entry with non-zero size.
// Otherwise, we use two entries, one entry has type TRACE_TYPE_*_FLUSH for
// the start address of flush, and one entry has type TRACE_TYPE_*_FLUSH_END
// for the end address (exclusive) of flush.
// The size field of both entries should be 0.
```

This is done for online traces, but offline traces fail to check for size truncation and fail to use two entries in that case, instead blindly truncating the size.