Improve error message in case of crashing SFC/SFB

Signed-off-by: Michael Buesch <m@bues.ch>
systemblocks: Also resolve STAT fields

Signed-off-by: Michael Buesch <m@bues.ch>
Implement SFB0 "CTU" IEC counter

Signed-off-by: Michael Buesch <m@bues.ch>