[AVX-512][InstCombine] Teach InstCombineCalls how to simplify demanded...

[AVX-512][InstCombine] Teach InstCombineCalls how to simplify demanded elements for scalar add,div,mul,sub,max,min intrinsics with masking and rounding.

These intrinsics don't read the upper bits of their second input. And the third input is the passthru for masking and that only uses the lower element as well.

llvm-svn: 289370