[AVX512] The vpermi2 instructions require an integer vector for the index...

[AVX512] The vpermi2 instructions require an integer vector for the index vector. This is reflected correctly in the intrinsics, but was not refelected in the isel patterns.

For the floating point types, this requires adding a bitcast to the index vector when its passed through to the output.

llvm-svn: 254277