vexriscv: reset wishbone bus on CPU reset

vexriscv: reset wishbone bus on CPU reset

If the CPU is resetting during a Wishbone transfer, assert the ERR line.

Because the resetOut line is likely multiple cycles long, this should
give Wishbone enough time to finish its transfer, which will cause d.stb
and i.stb to go to 0, which will return d_err and i_err to 0.

Signed-off-by: Sean Cross <sean@xobs.io>