LoongArch: Add tls transition support.

LoongArch: Add tls transition support.

Transitions between DESC->IE/LE and IE->LE are supported now.
1. For DESC -> LE:
   pcalau12i  $a0,%desc_pc_hi20(var)     =>  lu12i.w $a0,%le_hi20(var)
   addi.d     $a0,$a0,%desc_pc_lo12(var) =>  ori $a0,$a0,%le_lo12(var)
   ld.d       $a1,$a0,%desc_ld(var)      =>  NOP
   jirl       $ra,$a1,%desc_call(var)	 =>  NOP
   add.d      $a0,$a0,$tp
2. For DESC -> IE:
   pcalau12i  $a0,%desc_pc_hi20(var)     =>  pcalau12i $a0,%ie_pc_hi20(var)
   addi.d     $a0,$a0,%desc_pc_lo12(var) =>  ld.d $a0,$a0,%ie_pc_lo12(var)
   ld.d       $a1,$a0,%desc_ld(var)      =>  NOP
   jirl       $ra,$a1,%desc_call(var)	 =>  NOP
   add.d      $a0,$a0,$tp
3. For IE -> LE:
   pcalau12i  $a0,%ie_pc_hi20(var)       =>  lu12i.w $a0,%le_hi20(var)
   ld.d       $a0,$a0,%ie_pc_lo12(var)   =>  ori $a0,$a0,%le_lo12(var)
   add.d      $a0,$a0,$tp
4. When a tls variable is accessed using both DESC and IE, DESC transitions
   to IE and uses the same GOT entry as IE.