Fix require_vector_vs checking by reverting 66c4853

The require_vector_vs, i.e., sstatus_csr_t::enabled(SSTATUS_VS), was
expected to provide has_any_vector() check [1]. Unfortunately, a
previous commit [2] made the sstatus_csr_t::enabled(SSTATUS_VS) true
without any vector extension.

The previous commit [2] was for P-extension, which has been removed from
Spike [3].

This commit reverts the commit [2] and corrects require_vector_vs [1].

[1] a484f6e
[2] 66c4853
[3] #1660

Author: YenHaoChen

riscv/csrs.cc

@@ -642,11 +642,6 @@ bool sstatus_csr_t::enabled(const reg_t which) {
     if (!state->v || (virt_sstatus->read() & which) != 0)
       return true;
   }
-
-  // If the field doesn't exist, it is always enabled. See #823.
-  if (!orig_sstatus->field_exists(which))
-    return true;
-
   return false;
 }