The instruction DEXT may be transformed into DEXTU or DEXTM depending

The instruction DEXT may be transformed into DEXTU or DEXTM depending
on the size of the extraction and its position in the 64 bit word.

This patch allows support of the dext transformations with mips64 direct
object output.

0 <= msb < 32 0 <= lsb < 32 0 <= pos < 32 1 <= size <= 32
DINS
The field is entirely contained in the right-most word of the doubleword

32 <= msb < 64 0 <= lsb < 32 0 <= pos < 32 2 <= size <= 64
DINSM
The field straddles the words of the doubleword

32 <= msb < 64 32 <= lsb < 64 32 <= pos < 64 1 <= size <= 32
DINSU
The field is entirely contained in the left-most word of the doubleword

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162782 91177308-0d34-0410-b5e6-96231b3b80d8