fuzz: Increase search space for unusual pin changes

We now search 64 bytes for changes.  Additionally, we will flip up
to 8 SFRs in one go, rather than limiting it to 5 SFRs.
sd: Fix debug pin states

Now we fix DAT0 and DAT3 to be high.  For no particular reason, we fix
DAT1 and DAT2 to be low.  This removes random variability that doesn't
seem to affect anything.
fpga-config: Remove path, and make more robust

Now we require the FPGA bitstream file to be specified.