In generic cpu model, there are only low 16 registers and little 32-bit instruction. CK801 is the cpu
family with least basic features like generic model.
Add test run and check for generic cpu model in original test case to cover basic LLVM IR functionality.
CSKY arch has multiple FPU instruction versions such as FPU, FPUv2 and FPUv3 to implement floating operations.
For now, we just only support FPUv2 and FPUv3.
It includes the encoding, asm parsing of instructions and codegen of DAG nodes.
Loading constants inline is expensive on CSKY and it's in general better
to place the constant nearby in code space and then it can be loaded with a
simple 16/32 bit load instruction like lrw.
It needs lift or duplicates constant pool entry to make constant nearby so that lrw instruction can reach.
