[pk,sim,xcc] get rid of at register, introduce tp register

riscv/insns/mfcr.h

@@ -11,8 +11,7 @@ switch(insn.rtype.rs2)
     break;
 
   case 29:
-    val = tid;
+    throw trap_illegal_instruction;
-    break;
 
   default:
     val = -1;

riscv/insns/mtcr.h

@@ -5,6 +5,5 @@ switch(insn.rtype.rs2)
     break;
 
   case 29:
-    tid = RS1;
+    throw trap_illegal_instruction;
-    break;
 }

riscv/processor.cc

@@ -19,7 +19,6 @@ processor_t::processor_t(sim_t* _sim, char* _mem, size_t _memsz)
   epc = 0;
   badvaddr = 0;
   cause = 0;
-  tid = 0;
   pcr_k0 = 0;
   pcr_k1 = 0;
   tohost = 0;

riscv/processor.h

@@ -39,7 +39,6 @@ private:
   uint32_t interrupts_pending;
 
   // unprivileged control registers
-  uint32_t tid;
   uint32_t fsr;
 
   // 32-bit or 64-bit mode (redundant with sr)