[X86][AVX512BF16] Add a few missing insert/extract patterns
These are really the same as the f16 (and i16) instructions, but we need
them for any type that can occur.
Merge commit 2e4e04c59043 from llvm-project (by Phoebe Wang):
[X86][BF16] Do not lower to VCVTNEPS2BF16 without AVX512VL (#86395)
Fixes: #86305
These should fix "fatal error: error in backend: Cannot select: t71:
v32bf16 = insert_subvector t67, t64, Constant:i32<16>" when building the
misc/ncnn port.
PR: 278305
Reported by: yuri
MFC after: 1 month
