[X86] Custom widen 128/256-bit vXi32 fp_to_uint on avx512f targets without avx512vl...

[X86] Custom widen 128/256-bit vXi32 fp_to_uint on avx512f targets without avx512vl. Similar for vXi64 on avx512dq without avx512vl.

Summary:
Previously we did this with isel patterns that used garbage in
the widened part of the source. But that's not valid for strictfp.
So now we custom widen and use zeroes for the widened elemens for
strictfp.

This replaces D71864.

Reviewers: RKSimon, spatel, andrew.w.kaylor, pengfei, LiuChen3

Reviewed By: pengfei

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71879