MIPS32: Improve and moderately clean up mterp.

Improvements:
- use seb, seh, ins on R2+
- use lsa, trunc.l.(s|d), cvt.(s|d).l, jic on R6
- shorter float/double comparison
- shorter float/double to int/long conversion
- fewer memory reads in float/double to int/long conversion
- remove unnecessary %break's and branches across breaks
- use branch delay slots more efficiently on R2

Test: booted MIPS32R2 in QEMU
Test: test-art-target-run-test-interpreter (MIPS32R2) on CI20
Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: test-art-target-run-test-interpreter (MIPS32R6) in QEMU

Change-Id: I9959bec08e20c2423deae31f71b523ad36b4be9a
diff --git a/runtime/interpreter/mterp/mips/op_const.S b/runtime/interpreter/mterp/mips/op_const.S
index c505761..bd9f873 100644
--- a/runtime/interpreter/mterp/mips/op_const.S
+++ b/runtime/interpreter/mterp/mips/op_const.S
@@ -1,9 +1,8 @@
-    # const vAA,                           /* +BBBBbbbb */
+    /* const vAA, +BBBBbbbb */
     GET_OPA(a3)                            #  a3 <- AA
     FETCH(a0, 1)                           #  a0 <- bbbb (low)
     FETCH(a1, 2)                           #  a1 <- BBBB (high)
     FETCH_ADVANCE_INST(3)                  #  advance rPC, load rINST
-    sll       a1, a1, 16
-    or        a0, a1, a0                   #  a0 <- BBBBbbbb
+    INSERT_HIGH_HALF(a0, a1)               #  a0 <- BBBBbbbb
     GET_INST_OPCODE(t0)                    #  extract opcode from rINST
     SET_VREG_GOTO(a0, a3, t0)              #  vAA <- a0