AVX-512: Fixed the "test" operation for i1 type

AVX-512: Fixed the "test" operation for i1 type

Using KORTESTW for comparison i1 value with zero was wrong since the instruction tests 16 bits.
KORTESTW may be used with KSHIFTL+KSHIFTR that clean the 15 upper bits.
I removed (X86cmp i1, 0) pattern and zero-extend i1 to i8 and then use TESTB.

There are some cases where i1 is in the mask register and the upper bits are already zeroed.
Then KORTESTW is the better solution, but it is subject for optimization.
Meanwhile, I'm fixing the correctness issue.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228916 91177308-0d34-0410-b5e6-96231b3b80d8