MIPS: Fix DCHECK failure in v8::internal::Assembler::seb()

- DCHECK(IsMipsArchVariant(kMips32r2) || IsMipsArchVariant(kMips32r6)) is failed.
- I tried not to select instruction kMipsSeb in case of kMips32r1.

R=ivica.bogosavljevic@mips.com

Bug: v8:8006
Change-Id: If07450b1a35b4e9cb608344e137c032381da224d
Reviewed-on: https://chromium-review.googlesource.com/1160073
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Ivica Bogosavljevic <ibogosavljevic@wavecomp.com>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54931}

AUTHORS

@@ -101,6 +101,7 @@ Kang-Hao (Kenny) Lu <kennyluck@csail.mit.edu>
 Karl Skomski <karl@skomski.com>
 Kevin Gibbons <bakkot@gmail.com>
 Kris Selden <kris.selden@gmail.com>
+Kyounga Ra <kyounga@alticast.com>
 Loo Rong Jie <loorongjie@gmail.com>
 Luis Reis <luis.m.reis@gmail.com>
 Luke Zarko <lukezarko@gmail.com>

src/compiler/mips/instruction-selector-mips.cc

@@ -534,7 +534,8 @@ void InstructionSelector::VisitWord32Shr(Node* node) {
 
 void InstructionSelector::VisitWord32Sar(Node* node) {
   Int32BinopMatcher m(node);
-  if (m.left().IsWord32Shl() && CanCover(node, m.left().node())) {
+  if ((IsMipsArchVariant(kMips32r2) || IsMipsArchVariant(kMips32r6)) &&
+      m.left().IsWord32Shl() && CanCover(node, m.left().node())) {
     Int32BinopMatcher mleft(m.left().node());
     if (m.right().HasValue() && mleft.right().HasValue()) {
       MipsOperandGenerator g(this);