X86: Pattern match scalar loads + vcvtph2ps into just vcvtph2ps.

vcvtph2ps only reads the lower 64 bits of the address passed to the
intrinsic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206579 91177308-0d34-0410-b5e6-96231b3b80d8