ARM64: Improve code generation for load integer immediate
ARM64: Improve code generation for load integer immediate

Add a special case for immediates that can be loaded in one "or" instruction.

Refactor the code that produces sequences of movz/movn/movk to be less
redundant and to choose the shortest sequence between the "movz" sequence
and the "movn" sequence.

gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml