This patch moves from using a hard coded number (4)

This patch moves from using a hard coded number (4)
for the number of bytes in a particular instruction
to using
   const MCInstrDesc &Desc = MCII.get(TmpInst.getOpcode());
   Desc.getSize()

This is necessary with the advent of 16 bit instructions with
mips16 and micromips. It is also puts Mips in compliance with
the other targets for getting instruction size.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165171 91177308-0d34-0410-b5e6-96231b3b80d8