Remove support for SOC FPGA drivers

[bsdjhb]

The drivers have been disconnected from the build since the removal of
the SOCFPGA kernel configs.

[bsdjhb]

I plan to do this upstream, this PR is mostly just to ensure our CI doesn't trip over anything. I do need to ensure this doesn't remove anything we depend on for our FPGA setups.

[bsdjhb]

@jonwoodruff, @bukinr I believe from the recent discussion on Slack, our modern FPGA images use VirtIO for I/O instead of Altera IP blocks, so that we don't use any of these drivers currently (including atse(4)) and that we don't plan on using them in the future?