[xcc, sim] added slei/sleui in lieu of slti/sltiu

Rationale was that since we have the datapath for rc = (ra < rb),
it's straightforward to also add rc = !(imm < rb) = (rb <= imm).

riscv/execute.h

@@ -480,12 +480,12 @@ switch((insn.bits >> 0x19) & 0x7f)
       }
       case 0x2:
       {
-        #include "insns/slti.h"
+        #include "insns/slei.h"
         break;
       }
       case 0x3:
       {
-        #include "insns/sltiu.h"
+        #include "insns/sleiu.h"
         break;
       }
       case 0x4:

riscv/insns/slei.h

@@ -0,0 +1 @@
+RA = !(sreg_t(cmp_trunc(SIMM)) < sreg_t(cmp_trunc(RB)));

riscv/insns/sleiu.h

@@ -0,0 +1 @@
+RA = !(cmp_trunc(SIMM) < cmp_trunc(RB));

riscv/insns/slti.h

@@ -1 +0,0 @@
-RA = sreg_t(cmp_trunc(RB)) < sreg_t(cmp_trunc(SIMM));

riscv/insns/sltiu.h

@@ -1 +0,0 @@
-RA = cmp_trunc(RB) < cmp_trunc(SIMM);