legalize senvcfg.CBIE

The value 2 of senvcfg.CBIE is reserved. This commit legalizes it to 0.

Reference: https://github.com/riscv/riscv-CMOs/issues/65

riscv/csrs.cc

@@ -1476,7 +1476,7 @@ void sstateen_csr_t::verify_permissions(insn_t insn, bool write) const {
 // implement class senvcfg_csr_t
 senvcfg_csr_t::senvcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask,
                              const reg_t init):
-  masked_csr_t(proc, addr, mask, init) {
+  envcfg_csr_t(proc, addr, mask, init) {
 }
 
 void senvcfg_csr_t::verify_permissions(insn_t insn, bool write) const {

riscv/csrs.h

@@ -759,7 +759,7 @@ class sstateen_csr_t: public hstateen_csr_t {
   virtual bool unlogged_write(const reg_t val) noexcept override;
 };
 
-class senvcfg_csr_t final: public masked_csr_t {
+class senvcfg_csr_t final: public envcfg_csr_t {
  public:
   senvcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask, const reg_t init);
   virtual void verify_permissions(insn_t insn, bool write) const override;