Support flexible memory configuration for FPGA

[tk26eng]

Now we have two configurations for buffers between CPU and FPGA.

One is a configuration which use /dev/mem for all buffers (threshold/kernel/input/output). Another is a configuration which threshold/kernel use /dev/mem and input/output use /dev/udmabuf{0, 1}.

But it is not flexible and hard to change memory assignment by sources because the sources of them is little messy. We need to provide easy way to change memory assignment and clean up sources around them.

[iizukak]

@tk26eng Good issue. Do you have any idea for this?