[inductor] Enable multilayer reductions with dynamic shapes (#106747)
Currently multilayer reduction (aka split reductions) are only used with static
shapes which results in worse performance and accuracy when dynamic shapes are
enabled. Instead, this only requires that the shape has a hint value.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106747
Approved by: https://github.com/lezcano
ghstack dependencies: #106626, #106870
