[MIPS] Remove warnings about use of at register

Also, don't restore k0 and k1 as part of long jump as they are reserved for
kernel usage.

Change-Id: I4eec9eb5d21de96ca79f2cef9407a0e19c9c2178
diff --git a/runtime/arch/mips/quick_entrypoints_mips.S b/runtime/arch/mips/quick_entrypoints_mips.S
index 95fcd73..96e0afd 100644
--- a/runtime/arch/mips/quick_entrypoints_mips.S
+++ b/runtime/arch/mips/quick_entrypoints_mips.S
@@ -298,7 +298,11 @@
     l.s     $f29, 116($a1)
     l.s     $f30, 120($a1)
     l.s     $f31, 124($a1)
+    .set push
+    .set nomacro
+    .set noat
     lw      $at, 4($a0)
+    .set pop
     lw      $v0, 8($a0)
     lw      $v1, 12($a0)
     lw      $a1, 20($a0)
@@ -322,8 +326,6 @@
     lw      $s7, 92($a0)
     lw      $t8, 96($a0)
     lw      $t9, 100($a0)
-    lw      $k0, 104($a0)
-    lw      $k1, 108($a0)
     lw      $gp, 112($a0)
     lw      $sp, 116($a0)
     lw      $fp, 120($a0)