Fixed the SS42AI template for the SSE 4.2 instructions with TA prefix so it does

Fixed the SS42AI template for the SSE 4.2 instructions with TA prefix so it does
not get an "Unknown immediate size" assert failure when used.  All instructions
of this form have an 8-bit immediate.  Also added a test case of an example
instruction that is of this form.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99435 91177308-0d34-0410-b5e6-96231b3b80d8