legalize henvcfg.CBIE

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

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

riscv/csrs.cc

@@ -916,7 +916,7 @@ bool envcfg_csr_t::unlogged_write(const reg_t val) noexcept {
 
 // implement class henvcfg_csr_t
 henvcfg_csr_t::henvcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask, const reg_t init, csr_t_p menvcfg):
-  masked_csr_t(proc, addr, mask, init),
+  envcfg_csr_t(proc, addr, mask, init),
   menvcfg(menvcfg) {
 }
 

riscv/csrs.h

@@ -468,7 +468,7 @@ class envcfg_csr_t: public masked_csr_t {
 // henvcfg.pbmte is read_only 0 when menvcfg.pbmte = 0
 // henvcfg.stce is read_only 0 when menvcfg.stce = 0
 // henvcfg.hade is read_only 0 when menvcfg.hade = 0
-class henvcfg_csr_t final: public masked_csr_t {
+class henvcfg_csr_t final: public envcfg_csr_t {
  public:
   henvcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask, const reg_t init, csr_t_p menvcfg);