Ghidra-based AVR Lifter

[ivg]

Current State

Since LLVM is not yet ready for AVR we switched to Ghidra. We still have to use LLVM as a loader (and it proves to fail on AVR as well, but we addressed it). The lifter and decode work well so far, but we lack good testing binaries to be sure about that. The data model of the lifter (namely the registers) is not yet clear.

We will try adding some tests before merging.