Adds a missing state transition that was causing restoration of the wrong value to scratch mask k0. This was resulting in a ERROR: expected k0 == 0xffff, but is 0xd360 error in the drx-scattergather app.
Postpones updating trace buffer ptr in the memval_simple sample client to post-write. This is to mitigate cases when the write buffer doesn't get written to due to the app write segfaulting, which results in no matching entry in the write buffer for the trace buffer entry. This causes an assert failure later write_base <= write_ptr in trace_fault.
Adds a test that runs the drx-scattergather app under the memval_simple client to verify the above two fixes.
Issue: #2985 (closed)