[VPlan] Don't consider VPWidenCanonicalIVRecipe phi-like.

VPWidenCanonicalIVRecipe does not create PHI instructions, so it does
not need to be placed in the phi section of a VPBasicBlock.

Also tidies the code so the WidenCanonicalIV recipe and the
compare/lane-masks are created in the header.

Discussed D113223.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D116473