Disabling store buffer breaks LSU

[stffrdhrn]

The mor1kx_lsu_cappuccino write ack logic depends on writes to the store buffer to be acked.

If we disable the store buffer acks are not returned and the system does not run.

This can be tested using mor1k_lsu_cappuccino formal via editing mor1k_lsu_cappuccino.sby to disable the store buffer and run make -C bench/formal mor1k_lsu_cappuccino. Or it can be tested with fusesoc and mor1kx-generic running a simple hello world type program.