You need a bitforce enabled version of cgminer.
It's off by default.
So if you get it from github the compile steps are changed to:
CFLAGS="-O2 -Wall" ./configure --enable-bitforce
make
(i.e. the '--scan-serial auto' isn't needed if you just run a cgminer with bitforce code enabled - it will run an 'auto' anyway)
Fully missed that FPGA miners are not enabled with cgminer's default build options. With the current stampede to BFL devices I guess it is time to include FPGA support by default. But since e.g. scanning for an Icarus takes considerably long, it might be a good idea to require the "--scan-serial auto" parameter explicitly set to initiate discovery. Sadly, I'll have to wait for another 3 weeks for my devices to arrive and to test all of this