[SVE] Add intrinsics for integer binops that explicitly undefine the result for inactive lanes.

The intent is to lower the clang X form SVE builtins to these
intrinsics. The suffix _x is already in use to signify unpredicated
SVE intrinsics hence my choice to use _u to signify those intrinsics
where the result for inactive lanes is undefined.

Differential Revision: https://reviews.llvm.org/D141937