[AVX-512] Don't add an additional rounding mode operand to the avx512 vcvtps2ph intri...

[AVX-512] Don't add an additional rounding mode operand to the avx512 vcvtps2ph intrinsic lowering.

There was no way to control its value so it was always FROUND_CURRENT making it unnecessary. The true rounding mode is encoded in the immediate operand of the instruction.

This also removes the pattern from the rb form of the instructions since there is no way to specify the FROUND_NO_EXC rounding mode it required.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282052 91177308-0d34-0410-b5e6-96231b3b80d8