This basic parser will handle basic instructions with register or immediate operands.
With the addition of CSKYInstPrinter, we can now make use of lit tests.
Differential Revision: https://reviews.llvm.org/D93798
Add basis of CSKY MCTargetDesc and it's enough to compile and link but doesn't yet do anything particularly useful.
Once an ASM parser and printer are added in the next two patches, the whole thing can be usefully tested.
Differential Revision: https://reviews.llvm.org/D93372