Zicsr Extension

6 instructions in the Zicsr extension.

• csrrc — Atomic Read and Clear Bits in CSR
• csrrci — Atomic Read and Clear Bits in CSR with Immediate
• csrrs — Atomic Read and Set Bits in CSR
• csrrsi — Atomic Read and Set Bits in CSR with Immediate
• csrrw — Atomic Read/Write CSR
• csrrwi — Atomic Read/Write CSR Immediate