The FSRU (aka EISCAT) was never supported in UHD 4.0. The FPGA
repository never had the relevant files, and the block controller also
never existed. This removes all the corresponding files from MPM, as
well as some references from makefiles.
- Moved nijesdcore to cores/
- Moved udev, net, dtoverlay, uio to sys_utils/
- Made all imports non-relative (except in __init__.py files)
- Removed some unnecessary imports
- Reordered some imports for Python conventions
